diff --git a/lib/protobuf/field/bytes_field.rb b/lib/protobuf/field/bytes_field.rb
index 81a3634..e120835 100644
--- a/lib/protobuf/field/bytes_field.rb
+++ b/lib/protobuf/field/bytes_field.rb
@@ -48,7 +48,18 @@ module Protobuf
 
       def coerce!(value)
         case value
-        when String, Symbol
+        when String
+          if value.encoding == Encoding::ASCII_8BIT
+            # This is a "binary" string
+            value
+          else
+            # Assume the value is Base64 encoded (from JSON)
+            # Ideally we'd do the Base64 decoding while processing the JSON,
+            # but this is tricky to do since we don't know the protobuf field
+            # types when we do that.
+            Base64.decode64(value)
+          end
+        when Symbol
           value.to_s
         when NilClass
           nil
@@ -59,7 +70,7 @@ module Protobuf
         end
       end
 
-      def json_encode(value)
+      def json_encode(value, options={})
         Base64.strict_encode64(value)
       end
     end
diff --git a/lib/protobuf/field/enum_field.rb b/lib/protobuf/field/enum_field.rb
index 6993faf..12867ad 100644
--- a/lib/protobuf/field/enum_field.rb
+++ b/lib/protobuf/field/enum_field.rb
@@ -37,6 +37,11 @@ module Protobuf
         type_class.fetch(value) || fail(TypeError, "Invalid Enum value: #{value.inspect} for #{name}")
       end
 
+      def json_encode(value, options={})
+        enum = type_class.enums.find { |e| e.to_i == value }
+        enum.to_s(:name)
+      end
+
       private
 
       ##
diff --git a/lib/protobuf/field/field_array.rb b/lib/protobuf/field/field_array.rb
index e4f2eb1..47f9c37 100644
--- a/lib/protobuf/field/field_array.rb
+++ b/lib/protobuf/field/field_array.rb
@@ -49,14 +49,14 @@ module Protobuf
       # Return a hash-representation of the given values for this field type
       # that is safe to convert to JSON.
       # The value in this case would be an array.
-      def to_json_hash_value
+      def to_json_hash_value(options = {})
         if field.respond_to?(:json_encode)
           map do |value|
             field.json_encode(value)
           end
         else
           map do |value|
-            value.respond_to?(:to_json_hash_value) ? value.to_json_hash_value : value
+            value.respond_to?(:to_json_hash_value) ? value.to_json_hash_value(options) : value
           end
         end
       end
@@ -81,6 +81,8 @@ module Protobuf
 
         if field.is_a?(::Protobuf::Field::EnumField)
           field.type_class.fetch(value)
+        elsif field.is_a?(::Protobuf::Field::BytesField)
+          field.coerce!(value)
         elsif field.is_a?(::Protobuf::Field::MessageField) && value.is_a?(field.type_class)
           value
         elsif field.is_a?(::Protobuf::Field::MessageField) && value.respond_to?(:to_hash)
diff --git a/lib/protobuf/field/field_hash.rb b/lib/protobuf/field/field_hash.rb
index 36b2644..94eedbb 100644
--- a/lib/protobuf/field/field_hash.rb
+++ b/lib/protobuf/field/field_hash.rb
@@ -58,14 +58,14 @@ module Protobuf
       # The value in this case would be the hash itself, right? Unfortunately
       # not because the values of the map could be messages themselves that we
       # need to transform.
-      def to_json_hash_value
+      def to_json_hash_value(options = {})
         if field.respond_to?(:json_encode)
           each_with_object({}) do |(key, value), hash|
             hash[key] = field.json_encode(value)
           end
         else
           each_with_object({}) do |(key, value), hash|
-            hash[key] = value.respond_to?(:to_json_hash_value) ? value.to_json_hash_value : value
+            hash[key] = value.respond_to?(:to_json_hash_value) ? value.to_json_hash_value(options) : value
           end
         end
       end
diff --git a/lib/protobuf/field/int64_field.rb b/lib/protobuf/field/int64_field.rb
index 3b33889..f2597b2 100644
--- a/lib/protobuf/field/int64_field.rb
+++ b/lib/protobuf/field/int64_field.rb
@@ -29,6 +29,13 @@ module Protobuf
         return false
       end
 
+      def json_encode(value, options = {})
+        if options[:proto3]
+          value == 0 ? nil : value.to_s
+        else
+          value
+        end
+      end
     end
   end
 end
diff --git a/lib/protobuf/field/sint64_field.rb b/lib/protobuf/field/sint64_field.rb
index 2aba7df..0c1c085 100644
--- a/lib/protobuf/field/sint64_field.rb
+++ b/lib/protobuf/field/sint64_field.rb
@@ -16,6 +16,13 @@ module Protobuf
         INT64_MIN
       end
 
+      def json_encode(value, options = {})
+        if options[:proto3]
+          value == 0 ? nil : value.to_s
+        else
+          value
+        end
+      end
     end
   end
 end
diff --git a/lib/protobuf/field/string_field.rb b/lib/protobuf/field/string_field.rb
index 6c9c278..551bdd2 100644
--- a/lib/protobuf/field/string_field.rb
+++ b/lib/protobuf/field/string_field.rb
@@ -43,7 +43,7 @@ module Protobuf
         "#{::Protobuf::Field::VarintField.encode(value_to_encode.bytesize)}#{value_to_encode}"
       end
 
-      def json_encode(value)
+      def json_encode(value, options={})
         value
       end
     end
diff --git a/lib/protobuf/field/uint64_field.rb b/lib/protobuf/field/uint64_field.rb
index 8a060f1..df041fc 100644
--- a/lib/protobuf/field/uint64_field.rb
+++ b/lib/protobuf/field/uint64_field.rb
@@ -16,6 +16,13 @@ module Protobuf
         0
       end
 
+      def json_encode(value, options = {})
+        if options[:proto3]
+          value == 0 ? nil : value.to_s
+        else
+          value
+        end
+      end
     end
   end
 end
diff --git a/lib/protobuf/message.rb b/lib/protobuf/message.rb
index a13c0d1..eca075d 100644
--- a/lib/protobuf/message.rb
+++ b/lib/protobuf/message.rb
@@ -21,6 +21,22 @@ module Protobuf
       name
     end
 
+    def self.from_json(json)
+      fields = normalize_json(JSON.parse(json))
+      new(fields)
+    end
+
+    def self.normalize_json(ob)
+      case ob
+      when Array
+        ob.map { |value| normalize_json(value) }
+      when Hash
+        Hash[*ob.flat_map { |key, value| [key.underscore, normalize_json(value)] }]
+      else
+        ob
+      end
+    end
+
     ##
     # Constructor
     #
@@ -134,29 +150,36 @@ module Protobuf
     end
 
     def to_json(options = {})
-      to_json_hash.to_json(options)
+      to_json_hash(options).to_json(options)
     end
 
     # Return a hash-representation of the given fields for this message type that
     # is safe to convert to JSON.
-    def to_json_hash
+    def to_json_hash(options = {})
       result = {}
 
+      proto3 = options[:proto3] || options[:lower_camel_case]
+
       @values.each_key do |field_name|
         value = self[field_name]
         field = self.class.get_field(field_name, true)
 
         # NB: to_json_hash_value should come before json_encode so as to handle
         # repeated fields without extra logic.
-        hashed_value = if value.respond_to?(:to_json_hash_value)
-                         value.to_json_hash_value
+        hashed_value = if value.respond_to?(:to_json_hash_value) && !field.is_a?(::Protobuf::Field::EnumField)
+                         value.to_json_hash_value(options)
                        elsif field.respond_to?(:json_encode)
-                         field.json_encode(value)
+                         field.json_encode(value, options)
                        else
                          value
                        end
 
-        result[field.name] = hashed_value
+        if proto3 && (hashed_value.nil? || value == field.class.default)
+          result.delete(field.name)
+        else
+          key = proto3 ? field.name.to_s.camelize(:lower).to_sym : field.name
+          result[key] = hashed_value
+        end
       end
 
       result
diff --git a/spec/encoding/all_types_spec.rb b/spec/encoding/all_types_spec.rb
index fbd38b4..04ddb86 100644
--- a/spec/encoding/all_types_spec.rb
+++ b/spec/encoding/all_types_spec.rb
@@ -18,7 +18,7 @@ RSpec.describe ::Protobuf do
       :optional_double => 112,
       :optional_bool => true,
       :optional_string => "115",
-      :optional_bytes => "116",
+      :optional_bytes => "116".force_encoding(Encoding::ASCII_8BIT),
       :optional_nested_message => Protobuf_unittest::TestAllTypes::NestedMessage.new(:bb => 118),
       :optional_foreign_message => Protobuf_unittest::ForeignMessage.new(:c => 119),
       :optional_import_message => Protobuf_unittest_import::ImportMessage.new(:d => 120),
@@ -43,7 +43,7 @@ RSpec.describe ::Protobuf do
       :repeated_double => [212, 312],
       :repeated_bool => [true, false],
       :repeated_string => ["215", "315"],
-      :repeated_bytes => ["216", "316"],
+      :repeated_bytes => ["216".force_encoding(Encoding::ASCII_8BIT), "316".force_encoding(Encoding::ASCII_8BIT)],
       :repeated_nested_message => [
         ::Protobuf_unittest::TestAllTypes::NestedMessage.new(:bb => 218),
         ::Protobuf_unittest::TestAllTypes::NestedMessage.new(:bb => 318),
@@ -88,7 +88,7 @@ RSpec.describe ::Protobuf do
       :default_double => 412,
       :default_bool => false,
       :default_string => "415",
-      :default_bytes => "416",
+      :default_bytes => "416".force_encoding(Encoding::ASCII_8BIT),
       :default_nested_enum => ::Protobuf_unittest::TestAllTypes::NestedEnum::FOO,
       :default_foreign_enum => ::Protobuf_unittest::ForeignEnum::FOREIGN_FOO,
       :default_import_enum => ::Protobuf_unittest_import::ImportEnum::IMPORT_FOO,
diff --git a/spec/encoding/extreme_values_spec.rb b/spec/encoding/extreme_values_spec.rb
index 477e695..7f3d516 100644
Binary files a/spec/encoding/extreme_values_spec.rb and b/spec/encoding/extreme_values_spec.rb differ
diff --git a/spec/lib/protobuf/field/enum_field_spec.rb b/spec/lib/protobuf/field/enum_field_spec.rb
index cd72760..c2e04ee 100644
--- a/spec/lib/protobuf/field/enum_field_spec.rb
+++ b/spec/lib/protobuf/field/enum_field_spec.rb
@@ -23,4 +23,22 @@ RSpec.describe Protobuf::Field::EnumField do
       expect(message.decode(instance.encode).enum).to eq(-33)
     end
   end
+
+  # https://developers.google.com/protocol-buffers/docs/proto3#json
+  describe '.{to_json, from_json}' do
+    it 'serialises enum value as string' do
+      instance = message.new(:enum => :POSITIVE)
+      expect(instance.to_json).to eq('{"enum":"POSITIVE"}')
+    end
+
+    it 'deserialises enum value as integer' do
+      instance = message.from_json('{"enum":22}')
+      expect(instance.enum).to eq(22)
+    end
+
+    it 'deserialises enum value as string' do
+      instance = message.from_json('{"enum":"NEGATIVE"}')
+      expect(instance.enum).to eq(-33)
+    end
+  end
 end
diff --git a/spec/lib/protobuf/field/fixed64_field_spec.rb b/spec/lib/protobuf/field/fixed64_field_spec.rb
index d7feb12..00ad743 100644
--- a/spec/lib/protobuf/field/fixed64_field_spec.rb
+++ b/spec/lib/protobuf/field/fixed64_field_spec.rb
@@ -4,4 +4,30 @@ RSpec.describe Protobuf::Field::Fixed64Field do
 
   it_behaves_like :packable_field, described_class
 
+  let(:message) do
+    Class.new(::Protobuf::Message) do
+      optional :fixed64, :some_field, 1
+    end
+  end
+
+  # https://developers.google.com/protocol-buffers/docs/proto3#json
+  describe '.{to_json, from_json}' do
+    it 'serialises 0' do
+      instance = message.new(some_field: 0)
+      expect(instance.to_json(proto3: true)).to eq('{}')
+      expect(instance.to_json).to eq('{"some_field":0}')
+    end
+
+    it 'serialises max value' do
+      instance = message.new(some_field: described_class.max)
+      expect(instance.to_json(proto3: true)).to eq('{"someField":"18446744073709551615"}')
+      expect(instance.to_json).to eq('{"some_field":18446744073709551615}')
+    end
+
+    it 'serialises min value' do
+      instance = message.new(some_field: described_class.min)
+      expect(instance.to_json(proto3: true)).to eq('{}')
+      expect(instance.to_json).to eq('{"some_field":0}')
+    end
+  end
 end
diff --git a/spec/lib/protobuf/field/int64_field_spec.rb b/spec/lib/protobuf/field/int64_field_spec.rb
index 1bbe7c0..d0c77d3 100644
--- a/spec/lib/protobuf/field/int64_field_spec.rb
+++ b/spec/lib/protobuf/field/int64_field_spec.rb
@@ -4,4 +4,30 @@ RSpec.describe Protobuf::Field::Int64Field do
 
   it_behaves_like :packable_field, described_class
 
+  let(:message) do
+    Class.new(::Protobuf::Message) do
+      optional :int64, :some_field, 1
+    end
+  end
+
+  # https://developers.google.com/protocol-buffers/docs/proto3#json
+  describe '.{to_json, from_json}' do
+    it 'serialises 0' do
+      instance = message.new(some_field: 0)
+      expect(instance.to_json(proto3: true)).to eq('{}')
+      expect(instance.to_json).to eq('{"some_field":0}')
+    end
+
+    it 'serialises max value' do
+      instance = message.new(some_field: described_class.max)
+      expect(instance.to_json(proto3: true)).to eq('{"someField":"9223372036854775807"}')
+      expect(instance.to_json).to eq('{"some_field":9223372036854775807}')
+    end
+
+    it 'serialises min value' do
+      instance = message.new(some_field: described_class.min)
+      expect(instance.to_json(proto3: true)).to eq('{"someField":"-9223372036854775808"}')
+      expect(instance.to_json).to eq('{"some_field":-9223372036854775808}')
+    end
+  end
 end
diff --git a/spec/lib/protobuf/field/sfixed64_field_spec.rb b/spec/lib/protobuf/field/sfixed64_field_spec.rb
index f380ed5..7988f45 100644
--- a/spec/lib/protobuf/field/sfixed64_field_spec.rb
+++ b/spec/lib/protobuf/field/sfixed64_field_spec.rb
@@ -6,4 +6,30 @@ RSpec.describe Protobuf::Field::Sfixed64Field do
     let(:value) { [-1, 0, 1] }
   end
 
+  let(:message) do
+    Class.new(::Protobuf::Message) do
+      optional :sfixed64, :some_field, 1
+    end
+  end
+
+  # https://developers.google.com/protocol-buffers/docs/proto3#json
+  describe '.{to_json, from_json}' do
+    it 'serialises 0' do
+      instance = message.new(some_field: 0)
+      expect(instance.to_json(proto3: true)).to eq('{}')
+      expect(instance.to_json).to eq('{"some_field":0}')
+    end
+
+    it 'serialises max value' do
+      instance = message.new(some_field: described_class.max)
+      expect(instance.to_json(proto3: true)).to eq('{"someField":"9223372036854775807"}')
+      expect(instance.to_json).to eq('{"some_field":9223372036854775807}')
+    end
+
+    it 'serialises min value as string' do
+      instance = message.new(some_field: described_class.min)
+      expect(instance.to_json(proto3: true)).to eq('{"someField":"-9223372036854775808"}')
+      expect(instance.to_json).to eq('{"some_field":-9223372036854775808}')
+    end
+  end
 end
diff --git a/spec/lib/protobuf/field/sint64_field_spec.rb b/spec/lib/protobuf/field/sint64_field_spec.rb
index 84ca730..e6fc05f 100644
--- a/spec/lib/protobuf/field/sint64_field_spec.rb
+++ b/spec/lib/protobuf/field/sint64_field_spec.rb
@@ -6,4 +6,30 @@ RSpec.describe Protobuf::Field::Sint64Field do
     let(:value) { [-1, 0, 1] }
   end
 
+  let(:message) do
+    Class.new(::Protobuf::Message) do
+      optional :sint64, :some_field, 1
+    end
+  end
+
+  # https://developers.google.com/protocol-buffers/docs/proto3#json
+  describe '.{to_json, from_json}' do
+    it 'serialises 0' do
+      instance = message.new(some_field: 0)
+      expect(instance.to_json(proto3: true)).to eq('{}')
+      expect(instance.to_json).to eq('{"some_field":0}')
+    end
+
+    it 'serialises max value as string' do
+      instance = message.new(some_field: described_class.max)
+      expect(instance.to_json(proto3: true)).to eq('{"someField":"9223372036854775807"}')
+      expect(instance.to_json).to eq('{"some_field":9223372036854775807}')
+    end
+
+    it 'serialises min value as string' do
+      instance = message.new(some_field: described_class.min)
+      expect(instance.to_json(proto3: true)).to eq('{"someField":"-9223372036854775808"}')
+      expect(instance.to_json).to eq('{"some_field":-9223372036854775808}')
+    end
+  end
 end
diff --git a/spec/lib/protobuf/field/uint64_field_spec.rb b/spec/lib/protobuf/field/uint64_field_spec.rb
index 61b8d1b..90bc030 100644
--- a/spec/lib/protobuf/field/uint64_field_spec.rb
+++ b/spec/lib/protobuf/field/uint64_field_spec.rb
@@ -4,4 +4,30 @@ RSpec.describe Protobuf::Field::Uint64Field do
 
   it_behaves_like :packable_field, described_class
 
+  let(:message) do
+    Class.new(::Protobuf::Message) do
+      optional :uint64, :some_field, 1
+    end
+  end
+
+  # https://developers.google.com/protocol-buffers/docs/proto3#json
+  describe '.{to_json, from_json}' do
+    it 'serialises 0' do
+      instance = message.new(some_field: 0)
+      expect(instance.to_json(proto3: true)).to eq('{}')
+      expect(instance.to_json).to eq('{"some_field":0}')
+    end
+
+    it 'serialises max value' do
+      instance = message.new(some_field: described_class.max)
+      expect(instance.to_json(proto3: true)).to eq('{"someField":"18446744073709551615"}')
+      expect(instance.to_json).to eq('{"some_field":18446744073709551615}')
+    end
+
+    it 'serialises min value' do
+      instance = message.new(some_field: described_class.min)
+      expect(instance.to_json(proto3: true)).to eq('{}')
+      expect(instance.to_json).to eq('{"some_field":0}')
+    end
+  end
 end
diff --git a/spec/lib/protobuf/message_spec.rb b/spec/lib/protobuf/message_spec.rb
index 96668b6..cd49753 100644
--- a/spec/lib/protobuf/message_spec.rb
+++ b/spec/lib/protobuf/message_spec.rb
@@ -429,7 +429,7 @@ RSpec.describe Protobuf::Message do
     specify { expect(subject.to_json).to eq '{"name":"Test Name","active":false}' }
 
     context 'for byte fields' do
-      let(:bytes) { "\x06\x8D1HP\x17:b" }
+      let(:bytes) { "\x06\x8D1HP\x17:b".force_encoding(Encoding::ASCII_8BIT) }
 
       subject do
         ::Test::ResourceFindRequest.new(:widget_bytes => [bytes])
@@ -437,6 +437,36 @@ RSpec.describe Protobuf::Message do
 
       specify { expect(subject.to_json).to eq '{"widget_bytes":["Bo0xSFAXOmI="]}' }
     end
+
+    context 'using lower camel case field names' do
+      let(:bytes) { "\x06\x8D1HP\x17:b".force_encoding(Encoding::ASCII_8BIT) }
+
+      subject do
+        ::Test::ResourceFindRequest.new(:widget_bytes => [bytes])
+      end
+
+      specify { expect(subject.to_json(:proto3 => true)).to eq '{"widgetBytes":["Bo0xSFAXOmI="]}' }
+    end
+  end
+
+  describe '.from_json' do
+    it 'decodes optional bytes field with base64' do
+      expected_single_bytes = "\x06\x8D1HP\x17:b".unpack('C*')
+      single_bytes = ::Test::ResourceFindRequest
+                     .from_json('{"singleBytes":"Bo0xSFAXOmI="}')
+                     .single_bytes.unpack('C*')
+
+      expect(single_bytes).to(eq(expected_single_bytes))
+    end
+
+    it 'decodes repeated bytes field with base64' do
+      expected_widget_bytes = ["\x06\x8D1HP\x17:b"].map { |s| s.unpack('C*') }
+      widget_bytes = ::Test::ResourceFindRequest
+                     .from_json('{"widgetBytes":["Bo0xSFAXOmI="]}')
+                     .widget_bytes.map { |s| s.unpack('C*') }
+
+      expect(widget_bytes).to(eq(expected_widget_bytes))
+    end
   end
 
   describe '.to_json' do
diff --git a/spec/support/protos/resource.pb.rb b/spec/support/protos/resource.pb.rb
index f81ef52..e765b1c 100644
--- a/spec/support/protos/resource.pb.rb
+++ b/spec/support/protos/resource.pb.rb
@@ -72,6 +72,7 @@ module Test
     optional :bool, :active, 2
     repeated :string, :widgets, 3
     repeated :bytes, :widget_bytes, 4
+    optional :bytes, :single_bytes, 5
   end
 
   class ResourceSleepRequest
@@ -169,4 +170,3 @@ module Test
   end
 
 end
-
diff --git a/spec/support/protos/resource.proto b/spec/support/protos/resource.proto
index 70b338b..a5573e2 100644
--- a/spec/support/protos/resource.proto
+++ b/spec/support/protos/resource.proto
@@ -47,6 +47,7 @@ message ResourceFindRequest {
   optional bool active = 2;
   repeated string widgets = 3;
   repeated bytes widget_bytes = 4;
+  optional bytes single_bytes = 5;
 }
 
 message ResourceSleepRequest {
--- a/spec/encoding/extreme_values_spec.rb	2021-03-16 09:59:12.864960277 +0100
+++ b/spec/encoding/extreme_values_spec.rb	2021-03-12 18:22:09.951286951 +0100
@@ -4,7 +4,7 @@
 RSpec.describe ::Protobuf do
   it "correctly encodes extreme values" do
     message = Protobuf_unittest::TestExtremeDefaultValues.new(
-      :escaped_bytes => "\0\001\a\b\f\n\r\t\v\\\'\"\xfe",
+      :escaped_bytes => "\0\001\a\b\f\n\r\t\v\\\'\"\xfe".force_encoding(Encoding::ASCII_8BIT),
       :large_uint32 => 4294967295,
       :large_uint64 => 18446744073709551615,
       :small_int32 => -2147483647,
@@ -27,7 +27,7 @@
       :really_small_int32 => -2147483648,
       :really_small_int64 => -9223372036854775808,
       :string_with_zero => "hello",
-      :bytes_with_zero => "world",
+      :bytes_with_zero => "world".force_encoding(Encoding::ASCII_8BIT),
       :string_piece_with_zero => "abc",
       :cord_with_zero => "123",
     )