diff --git a/Rakefile b/Rakefile
index def6fd625..7c629c8a6 100644
--- a/Rakefile
+++ b/Rakefile
@@ -9,3 +9,10 @@ Rake::TestTask.new do |t|
 end
 
 task default: :test
+
+desc 'Run benchmarks'
+namespace :test do
+  Rake::TestTask.new(:benchmark) do |t|
+    t.pattern = 'test/benchmark/*_benchmark.rb'
+  end
+end
diff --git a/jsonapi-resources.gemspec b/jsonapi-resources.gemspec
index f9b7b05a5..cedf4b174 100644
--- a/jsonapi-resources.gemspec
+++ b/jsonapi-resources.gemspec
@@ -25,5 +25,7 @@ Gem::Specification.new do |spec|
   spec.add_development_dependency 'minitest-spec-rails'
   spec.add_development_dependency 'simplecov'
   spec.add_development_dependency 'pry'
+  spec.add_development_dependency 'concurrent-ruby-ext'
   spec.add_dependency 'rails', '>= 4.0'
+  spec.add_dependency 'concurrent-ruby'
 end
diff --git a/lib/jsonapi-resources.rb b/lib/jsonapi-resources.rb
index 6bd727a21..741be7b29 100644
--- a/lib/jsonapi-resources.rb
+++ b/lib/jsonapi-resources.rb
@@ -1,3 +1,4 @@
+require 'jsonapi/naive_cache'
 require 'jsonapi/resource'
 require 'jsonapi/response_document'
 require 'jsonapi/acts_as_resource_controller'
diff --git a/lib/jsonapi/acts_as_resource_controller.rb b/lib/jsonapi/acts_as_resource_controller.rb
index c609a82a8..42fa2b40e 100644
--- a/lib/jsonapi/acts_as_resource_controller.rb
+++ b/lib/jsonapi/acts_as_resource_controller.rb
@@ -113,7 +113,7 @@ def serialization_options
     #     JSONAPI.configuration.route = :camelized_route
     #
     # Override if you want to set a per controller key format.
-    # Must return a class derived from KeyFormatter.
+    # Must return an instance of a class derived from KeyFormatter.
     def key_formatter
       JSONAPI.configuration.key_formatter
     end
diff --git a/lib/jsonapi/configuration.rb b/lib/jsonapi/configuration.rb
index d54de4109..a5c715d30 100644
--- a/lib/jsonapi/configuration.rb
+++ b/lib/jsonapi/configuration.rb
@@ -1,14 +1,13 @@
 require 'jsonapi/formatter'
 require 'jsonapi/operations_processor'
 require 'jsonapi/active_record_operations_processor'
+require 'concurrent'
 
 module JSONAPI
   class Configuration
     attr_reader :json_key_format,
                 :resource_key_type,
-                :key_formatter,
                 :route_format,
-                :route_formatter,
                 :raise_if_parameters_not_allowed,
                 :operations_processor,
                 :allow_include,
@@ -23,7 +22,8 @@ class Configuration
                 :top_level_meta_record_count_key,
                 :exception_class_whitelist,
                 :always_include_to_one_linkage_data,
-                :always_include_to_many_linkage_data
+                :always_include_to_many_linkage_data,
+                :cache_formatters
 
     def initialize
       #:underscored_key, :camelized_key, :dasherized_key, or custom
@@ -74,20 +74,69 @@ def initialize
       # NOTE: always_include_to_many_linkage_data is not currently implemented
       self.always_include_to_one_linkage_data = false
       self.always_include_to_many_linkage_data = false
+
+      # Formatter Caching
+      # Set to false to disable caching of string operations on keys and links.
+      self.cache_formatters = true
+    end
+
+    def cache_formatters=(bool)
+      @cache_formatters = bool
+      if bool
+        @key_formatter_tlv = Concurrent::ThreadLocalVar.new
+        @route_formatter_tlv = Concurrent::ThreadLocalVar.new
+      else
+        @key_formatter_tlv = nil
+        @route_formatter_tlv = nil
+      end
     end
 
     def json_key_format=(format)
       @json_key_format = format
-      @key_formatter = JSONAPI::Formatter.formatter_for(format)
+      if @cache_formatters
+        @key_formatter_tlv = Concurrent::ThreadLocalVar.new
+      end
+    end
+
+    def route_format=(format)
+      @route_format = format
+      if @cache_formatters
+        @route_formatter_tlv = Concurrent::ThreadLocalVar.new
+      end
+    end
+
+    def key_formatter
+      if self.cache_formatters
+        formatter = @key_formatter_tlv.value
+        return formatter if formatter
+      end
+
+      formatter = JSONAPI::Formatter.formatter_for(self.json_key_format)
+
+      if self.cache_formatters
+        formatter = @key_formatter_tlv.value = formatter.cached
+      end
+
+      return formatter
     end
 
     def resource_key_type=(key_type)
       @resource_key_type = key_type
     end
 
-    def route_format=(format)
-      @route_format = format
-      @route_formatter = JSONAPI::Formatter.formatter_for(format)
+    def route_formatter
+      if self.cache_formatters
+        formatter = @route_formatter_tlv.value
+        return formatter if formatter
+      end
+
+      formatter = JSONAPI::Formatter.formatter_for(self.route_format)
+
+      if self.cache_formatters
+        formatter = @route_formatter_tlv.value = formatter.cached
+      end
+
+      return formatter
     end
 
     def operations_processor=(operations_processor)
diff --git a/lib/jsonapi/formatter.rb b/lib/jsonapi/formatter.rb
index 9965a7ac3..9da13cf86 100644
--- a/lib/jsonapi/formatter.rb
+++ b/lib/jsonapi/formatter.rb
@@ -9,9 +9,12 @@ def unformat(arg)
         arg
       end
 
+      def cached
+        return FormatterWrapperCache.new(self)
+      end
+
       def formatter_for(format)
-        formatter_class_name = "#{format.to_s.camelize}Formatter"
-        formatter_class_name.safe_constantize
+        "#{format.to_s.camelize}Formatter".safe_constantize
       end
     end
   end
@@ -51,11 +54,33 @@ def unformat(value)
       end
 
       def value_formatter_for(type)
-        formatter_name = "#{type.to_s.camelize}Value"
-        formatter_for(formatter_name)
+        "#{type.to_s.camelize}ValueFormatter".safe_constantize
       end
     end
   end
+
+  # Warning: Not thread-safe. Wrap in ThreadLocalVar as needed.
+  class FormatterWrapperCache
+    attr_reader :formatter_klass
+
+    def initialize(formatter_klass)
+      @formatter_klass = formatter_klass
+      @format_cache = NaiveCache.new{|arg| formatter_klass.format(arg) }
+      @unformat_cache = NaiveCache.new{|arg| formatter_klass.unformat(arg) }
+    end
+
+    def format(arg)
+      @format_cache.get(arg)
+    end
+
+    def unformat(arg)
+      @unformat_cache.get(arg)
+    end
+
+    def cached
+      self
+    end
+  end
 end
 
 class UnderscoredKeyFormatter < JSONAPI::KeyFormatter
diff --git a/lib/jsonapi/link_builder.rb b/lib/jsonapi/link_builder.rb
index 2ca5fef90..5ce94992a 100644
--- a/lib/jsonapi/link_builder.rb
+++ b/lib/jsonapi/link_builder.rb
@@ -2,21 +2,24 @@ module JSONAPI
   class LinkBuilder
     attr_reader :base_url,
                 :primary_resource_klass,
-                :route_formatter
+                :route_formatter,
+                :engine_name
 
     def initialize(config = {})
       @base_url               = config[:base_url]
       @primary_resource_klass = config[:primary_resource_klass]
       @route_formatter        = config[:route_formatter]
-      @is_engine              = !!engine_name
-    end
+      @engine_name            = build_engine_name
 
-    def engine?
-      @is_engine
+      # Warning: These make LinkBuilder non-thread-safe. That's not a problem with the
+      # request-specific way it's currently used, though.
+      @resources_path_cache   = JSONAPI::NaiveCache.new do |source_klass|
+        formatted_module_path_from_class(source_klass) + format_route(source_klass._type.to_s)
+      end
     end
 
-    def engine_name
-      @engine_name ||= build_engine_name
+    def engine?
+      !!@engine_name
     end
 
     def primary_resources_url
@@ -96,7 +99,7 @@ def engine_resources_path_name_from_class(klass)
     end
 
     def format_route(route)
-      route_formatter.format(route.to_s)
+      route_formatter.format(route)
     end
 
     def formatted_module_path_from_class(klass)
@@ -113,11 +116,12 @@ def module_scopes_from_class(klass)
       klass.name.to_s.split("::")[0...-1]
     end
 
+    def regular_resources_path(source_klass)
+      @resources_path_cache.get(source_klass)
+    end
+
     def regular_primary_resources_path
-      [
-        formatted_module_path_from_class(primary_resource_klass),
-        format_route(primary_resource_klass._type.to_s),
-      ].join
+      regular_resources_path(primary_resource_klass)
     end
 
     def regular_primary_resources_url
@@ -125,11 +129,7 @@ def regular_primary_resources_url
     end
 
     def regular_resource_path(source)
-      [
-        formatted_module_path_from_class(source.class),
-        format_route(source.class._type.to_s),
-        "/#{ source.id }",
-      ].join
+      "#{regular_resources_path(source.class)}/#{source.id}"
     end
 
     def regular_resource_url(source)
diff --git a/lib/jsonapi/naive_cache.rb b/lib/jsonapi/naive_cache.rb
new file mode 100644
index 000000000..53bf6ccb0
--- /dev/null
+++ b/lib/jsonapi/naive_cache.rb
@@ -0,0 +1,30 @@
+module JSONAPI
+
+  # Cache which memoizes the given block.
+  #
+  # It's "naive" because it clears the least-recently-inserted cache entry
+  # rather than the least-recently-used. This makes lookups faster but cache
+  # misses more frequent after cleanups. Therefore you the best time to use
+  # this cache is when you expect only a small number of unique lookup keys, so
+  # that the cache never has to clear.
+  #
+  # Also, it's not thread safe (although jsonapi-resources is careful to only
+  # use it in a thread safe way).
+  class NaiveCache
+    def initialize(cap = 10000, &calculator)
+      @cap = cap
+      @data = {}
+      @calculator = calculator
+    end
+
+    def get(key)
+      found = true
+      value = @data.fetch(key) { found = false }
+      return value if found
+      value = @calculator.call(key)
+      @data[key] = value
+      @data.shift if @data.length > @cap
+      return value
+    end
+  end
+end
diff --git a/lib/jsonapi/relationship.rb b/lib/jsonapi/relationship.rb
index 3d6492435..d03589e70 100644
--- a/lib/jsonapi/relationship.rb
+++ b/lib/jsonapi/relationship.rb
@@ -22,7 +22,7 @@ def primary_key
     end
 
     def resource_klass
-      @resource_klass = @parent_resource.resource_for(@class_name)
+      @resource_klass ||= @parent_resource.resource_for(@class_name)
     end
 
     def table_name
diff --git a/lib/jsonapi/resource.rb b/lib/jsonapi/resource.rb
index da89f4950..a4781f7ba 100644
--- a/lib/jsonapi/resource.rb
+++ b/lib/jsonapi/resource.rb
@@ -601,8 +601,10 @@ def find(filters, options = {})
         records = apply_pagination(records, options[:paginator], order_options)
 
         resources = []
+        resource_classes = {}
         records.each do |model|
-          resources.push self.resource_for_model(model).new(model, context)
+          resource_class = resource_classes[model.class] ||= self.resource_for_model(model)
+          resources.push resource_class.new(model, context)
         end
 
         resources
@@ -665,7 +667,7 @@ def key_type(key_type)
       end
 
       def resource_key_type
-        @_resource_key_type || JSONAPI.configuration.resource_key_type
+        @_resource_key_type ||= JSONAPI.configuration.resource_key_type
       end
 
       def verify_key(key, context = nil)
diff --git a/lib/jsonapi/resource_serializer.rb b/lib/jsonapi/resource_serializer.rb
index 421259b8d..0c82e3b90 100644
--- a/lib/jsonapi/resource_serializer.rb
+++ b/lib/jsonapi/resource_serializer.rb
@@ -12,7 +12,7 @@ class ResourceSerializer
     #     Purpose: determines which fields are serialized for a resource type. This encompasses both attributes and
     #              relationship ids in the links section for a resource. Fields are global for a resource type.
     #     Example: { people: [:id, :email, :comments], posts: [:id, :title, :author], comments: [:id, :body, :post]}
-    # key_formatter: KeyFormatter class to override the default configuration
+    # key_formatter: KeyFormatter instance to override the default configuration
     # serializer_options: additional options that will be passed to resource meta and links lambdas
 
     def initialize(primary_resource_klass, options = {})
@@ -21,12 +21,17 @@ def initialize(primary_resource_klass, options = {})
       @include            = options.fetch(:include, [])
       @include_directives = options[:include_directives]
       @key_formatter      = options.fetch(:key_formatter, JSONAPI.configuration.key_formatter)
+      @id_formatter       = ValueFormatter.value_formatter_for(:id)
       @link_builder       = generate_link_builder(primary_resource_klass, options)
       @always_include_to_one_linkage_data = options.fetch(:always_include_to_one_linkage_data,
                                                           JSONAPI.configuration.always_include_to_one_linkage_data)
       @always_include_to_many_linkage_data = options.fetch(:always_include_to_many_linkage_data,
                                                            JSONAPI.configuration.always_include_to_many_linkage_data)
       @serialization_options = options.fetch(:serialization_options, {})
+
+      # Warning: This makes ResourceSerializer non-thread-safe. That's not a problem with the
+      # request-specific way it's currently used, though.
+      @value_formatter_type_cache = NaiveCache.new{|arg| ValueFormatter.value_formatter_for(arg) }
     end
 
     # Converts a single resource, or an array of resources to a hash, conforming to the JSONAPI structure
@@ -81,8 +86,7 @@ def format_key(key)
     end
 
     def format_value(value, format)
-      value_formatter = JSONAPI::ValueFormatter.value_formatter_for(format)
-      value_formatter.format(value)
+      @value_formatter_type_cache.get(format).format(value)
     end
 
     private
@@ -300,18 +304,26 @@ def link_object(source, relationship, include_linkage = false)
     def foreign_key_value(source, relationship)
       foreign_key = relationship.foreign_key
       value = source.public_send(foreign_key)
-      IdValueFormatter.format(value)
+      @id_formatter.format(value)
     end
 
     def foreign_key_types_and_values(source, relationship)
       if relationship.is_a?(JSONAPI::Relationship::ToMany)
         if relationship.polymorphic?
-          source._model.public_send(relationship.name).pluck(:type, :id).map do |type, id|
-            [type.underscore.pluralize, IdValueFormatter.format(id)]
+          assoc = source._model.public_send(relationship.name)
+          # Avoid hitting the database again for values already pre-loaded
+          if assoc.respond_to?(:loaded?) and assoc.loaded?
+            assoc.map do |obj|
+              [obj.type.underscore.pluralize, @id_formatter.format(obj.id)]
+            end
+          else
+            assoc.pluck(:type, :id).map do |type, id|
+              [type.underscore.pluralize, @id_formatter.format(id)]
+            end
           end
         else
           source.public_send(relationship.foreign_key).map do |value|
-            [relationship.type, IdValueFormatter.format(value)]
+            [relationship.type, @id_formatter.format(value)]
           end
         end
       end
diff --git a/test/benchmark/request_benchmark.rb b/test/benchmark/request_benchmark.rb
new file mode 100644
index 000000000..7db5b25be
--- /dev/null
+++ b/test/benchmark/request_benchmark.rb
@@ -0,0 +1,14 @@
+require File.expand_path('../../test_helper', __FILE__)
+
+class RequestBenchmark < IntegrationBenchmark
+  def setup
+    $test_user = Person.find(1)
+  end
+
+  def bench_large_index_request
+    10.times do
+      get '/api/v2/books?include=bookComments,bookComments.author'
+      assert_jsonapi_response 200
+    end
+  end
+end
diff --git a/test/fixtures/books.yml b/test/fixtures/books.yml
index 667dd569b..87265107f 100644
--- a/test/fixtures/books.yml
+++ b/test/fixtures/books.yml
@@ -4,4 +4,4 @@ book_<%= book_num %>:
   title: Book <%= book_num %>
   isbn: 12345-<%= book_num %>-6789
   banned: <%= book_num > 600 && book_num < 700 %>
-<% end %>
\ No newline at end of file
+<% end %>
diff --git a/test/integration/requests/request_test.rb b/test/integration/requests/request_test.rb
index 992144cac..7f43e8323 100644
--- a/test/integration/requests/request_test.rb
+++ b/test/integration/requests/request_test.rb
@@ -12,11 +12,6 @@ def after_teardown
     JSONAPI.configuration.route_format = :underscored_route
   end
 
-  def assert_jsonapi_response(expected_status)
-    assert_equal JSONAPI::MEDIA_TYPE, response.content_type
-    assert_equal expected_status, status
-  end
-
   def test_get
     get '/posts'
     assert_jsonapi_response 200
diff --git a/test/test_helper.rb b/test/test_helper.rb
index 303409d65..44db43553 100644
--- a/test/test_helper.rb
+++ b/test/test_helper.rb
@@ -425,6 +425,25 @@ class ActiveSupport::TestCase
 class ActionDispatch::IntegrationTest
   self.fixture_path = "#{Rails.root}/fixtures"
   fixtures :all
+
+  def assert_jsonapi_response(expected_status)
+    assert_equal JSONAPI::MEDIA_TYPE, response.content_type
+    assert_equal expected_status, status
+  end
+end
+
+class IntegrationBenchmark < ActionDispatch::IntegrationTest
+  def self.runnable_methods
+    methods_matching(/^bench_/)
+  end
+
+  def self.run_one_method(klass, method_name, reporter)
+    Benchmark.bm(method_name.length) do |job|
+      job.report(method_name) do
+        super(klass, method_name, reporter)
+      end
+    end
+  end
 end
 
 class UpperCamelizedKeyFormatter < JSONAPI::KeyFormatter