diff --git a/benchmarks/boot_time_with_many_load_path_dirs.sh b/benchmarks/boot_time_with_many_load_path_dirs.sh
new file mode 100755
index 0000000000..09f5a8820a
--- /dev/null
+++ b/benchmarks/boot_time_with_many_load_path_dirs.sh
@@ -0,0 +1,123 @@
+ruby -v
+
+function run_benchmark_with_load_path_size {
+  pushd tmp
+  mkdir -p boot_time_benchmark
+
+  local load_path_size=$1
+  for (( i=0; i < $load_path_size; i++ )); do
+    mkdir -p "boot_time_benchmark/dir_$i"
+  done
+
+  local load_path=`ruby -e 'puts Array.new(Integer(ARGV.first)) { |i| "boot_time_benchmark/dir_#{i}" }.join(":")' $load_path_size`
+
+  echo "3 runs with $load_path_size dirs on load path, booting 50 times, using $2"
+  for i in {1..3}; do
+    time (for i in {1..50}; do ruby -I$load_path:../lib:../../rspec-support/lib -e 'require "rspec/core"'; done)
+  done
+  popd
+}
+
+run_benchmark_with_load_path_size 10   "require"
+run_benchmark_with_load_path_size 100  "require"
+run_benchmark_with_load_path_size 1000 "require"
+
+export REQUIRE_RELATIVE=1
+
+run_benchmark_with_load_path_size 10   "require_relative"
+run_benchmark_with_load_path_size 100  "require_relative"
+run_benchmark_with_load_path_size 1000 "require_relative"
+
+: <<'result_comment'
+ruby 2.0.0p247 (2013-06-27 revision 41674) [x86_64-darwin12.4.0]
+~/code/rspec-core/tmp ~/code/rspec-core
+3 runs with 10 dirs on load path, booting 50 times, using require
+
+real  0m3.815s
+user  0m3.205s
+sys 0m0.519s
+
+real  0m3.850s
+user  0m3.234s
+sys 0m0.527s
+
+real  0m3.840s
+user  0m3.225s
+sys 0m0.525s
+~/code/rspec-core
+~/code/rspec-core/tmp ~/code/rspec-core
+3 runs with 100 dirs on load path, booting 50 times, using require
+
+real  0m5.086s
+user  0m3.887s
+sys 0m1.107s
+
+real  0m5.063s
+user  0m3.870s
+sys 0m1.098s
+
+real  0m5.061s
+user  0m3.871s
+sys 0m1.097s
+~/code/rspec-core
+~/code/rspec-core/tmp ~/code/rspec-core
+3 runs with 1000 dirs on load path, booting 50 times, using require
+
+real  0m18.850s
+user  0m11.057s
+sys 0m7.679s
+
+real  0m18.783s
+user  0m11.012s
+sys 0m7.657s
+
+real  0m18.747s
+user  0m10.992s
+sys 0m7.639s
+~/code/rspec-core
+~/code/rspec-core/tmp ~/code/rspec-core
+3 runs with 10 dirs on load path, booting 50 times, using require_relative
+
+real  0m3.794s
+user  0m3.200s
+sys 0m0.506s
+
+real  0m3.769s
+user  0m3.180s
+sys 0m0.502s
+
+real  0m3.787s
+user  0m3.192s
+sys 0m0.502s
+~/code/rspec-core
+~/code/rspec-core/tmp ~/code/rspec-core
+3 runs with 100 dirs on load path, booting 50 times, using require_relative
+
+real  0m4.626s
+user  0m3.620s
+sys 0m0.910s
+
+real  0m4.652s
+user  0m3.642s
+sys 0m0.915s
+
+real  0m4.678s
+user  0m3.662s
+sys 0m0.924s
+~/code/rspec-core
+~/code/rspec-core/tmp ~/code/rspec-core
+3 runs with 1000 dirs on load path, booting 50 times, using require_relative
+
+real  0m14.400s
+user  0m8.615s
+sys 0m5.675s
+
+real  0m14.495s
+user  0m8.672s
+sys 0m5.711s
+
+real  0m14.541s
+user  0m8.705s
+sys 0m5.727s
+~/code/rspec-core
+result_comment
diff --git a/benchmarks/require_relative_v_require.rb b/benchmarks/require_relative_v_require.rb
index 944f74868e..04a5bafd8b 100644
--- a/benchmarks/require_relative_v_require.rb
+++ b/benchmarks/require_relative_v_require.rb
@@ -49,3 +49,27 @@
 # virtually no penalty
 #
 # ###################################
+
+__END__
+
+Ruby 2.0:
+
+➜  rspec-core git:(benchmark-require-relative) REQUIRE_RELATIVE=1 bundle exec ruby benchmarks/require_relative_v_require.rb
+   0.000000   0.030000   1.470000 (  1.481949)
+   0.000000   0.020000   1.440000 (  1.462620)
+   0.000000   0.020000   1.470000 (  1.491825)
+➜  rspec-core git:(benchmark-require-relative) bundle exec ruby benchmarks/require_relative_v_require.rb
+   0.000000   0.010000   1.510000 (  1.549906)
+   0.000000   0.010000   1.530000 (  1.546252)
+   0.000000   0.020000   1.510000 (  1.531644)
+
+Ruby 2.1:
+
+➜  rspec-core git:(benchmark-require-relative) bundle exec ruby benchmarks/require_relative_v_require.rb
+   0.000000   0.020000   1.570000 (  1.613217)
+   0.000000   0.020000   1.600000 (  1.618540)
+   0.010000   0.020000   1.570000 (  1.608205)
+➜  rspec-core git:(benchmark-require-relative) REQUIRE_RELATIVE=1 bundle exec ruby benchmarks/require_relative_v_require.rb
+   0.000000   0.020000   1.480000 (  1.515131)
+   0.000000   0.010000   1.480000 (  1.527766)
+   0.000000   0.020000   1.490000 (  1.515631)
diff --git a/lib/rspec/core.rb b/lib/rspec/core.rb
index f43032081e..c4251c9111 100644
--- a/lib/rspec/core.rb
+++ b/lib/rspec/core.rb
@@ -1,45 +1,39 @@
-require_rspec = if defined?(require_relative)
-  lambda do |path|
-    require_relative path
-  end
-else # for 1.8.7
-  lambda do |path|
-    require "rspec/#{path}"
-  end
-end
-
-require 'set'
 require 'time'
 require 'rbconfig'
 
-require_rspec['core/version']
-
-require 'rspec/support/caller_filter'
-require 'rspec/core/warnings'
-
-require_rspec['core/flat_map']
-require_rspec['core/filter_manager']
-require_rspec['core/dsl']
-require_rspec['core/notifications']
-require_rspec['core/reporter']
-
-require_rspec['core/hooks']
-require_rspec['core/memoized_helpers']
-require_rspec['core/metadata']
-require_rspec['core/pending']
-require_rspec['core/formatters']
-require_rspec['core/ordering']
-
-require_rspec['core/world']
-require_rspec['core/configuration']
-require_rspec['core/option_parser']
-require_rspec['core/configuration_options']
-require_rspec['core/command_line']
-require_rspec['core/runner']
-require_rspec['core/example']
-require_rspec['core/shared_example_group/collection']
-require_rspec['core/shared_example_group']
-require_rspec['core/example_group']
+require "rspec/support"
+RSpec::Support.require_rspec_support "caller_filter"
+
+RSpec::Support.define_optimized_require_for_rspec(:core) { |f| require_relative f }
+
+%w[
+  version
+  warnings
+
+  flat_map
+  filter_manager
+  dsl
+  notifications
+  reporter
+
+  hooks
+  memoized_helpers
+  metadata
+  pending
+  formatters
+  ordering
+
+  world
+  configuration
+  option_parser
+  configuration_options
+  command_line
+  runner
+  example
+  shared_example_group/collection
+  shared_example_group
+  example_group
+].each { |name| RSpec::Support.require_rspec_core name }
 
 module RSpec
   autoload :SharedContext, 'rspec/core/shared_context'
diff --git a/lib/rspec/core/configuration.rb b/lib/rspec/core/configuration.rb
index 8277a8a768..821b062155 100644
--- a/lib/rspec/core/configuration.rb
+++ b/lib/rspec/core/configuration.rb
@@ -1,7 +1,8 @@
 require 'fileutils'
-require 'rspec/core/backtrace_formatter'
-require 'rspec/core/ruby_project'
-require 'rspec/core/formatters/deprecation_formatter'
+
+RSpec::Support.require_rspec_core "backtrace_formatter"
+RSpec::Support.require_rspec_core "ruby_project"
+RSpec::Support.require_rspec_core "formatters/deprecation_formatter"
 
 module RSpec
   module Core
@@ -422,7 +423,7 @@ def mock_with(framework)
               "Pass a module or one of #{MOCKING_ADAPTERS.keys.inspect}"
           end
 
-          require "rspec/core/mocking_adapters/#{const_name.to_s.downcase}"
+          RSpec::Support.require_rspec_core "mocking_adapters/#{const_name.to_s.downcase}"
           RSpec::Core::MockingAdapters.const_get(const_name)
         end
 
diff --git a/lib/rspec/core/configuration_options.rb b/lib/rspec/core/configuration_options.rb
index 3a567e8088..85504e43b7 100644
--- a/lib/rspec/core/configuration_options.rb
+++ b/lib/rspec/core/configuration_options.rb
@@ -1,5 +1,6 @@
 require 'erb'
 require 'shellwords'
+require 'set'
 
 module RSpec
   module Core
diff --git a/lib/rspec/core/drb_command_line.rb b/lib/rspec/core/drb_command_line.rb
index 8f390d9276..db4ab648b8 100644
--- a/lib/rspec/core/drb_command_line.rb
+++ b/lib/rspec/core/drb_command_line.rb
@@ -1,5 +1,5 @@
 require 'drb/drb'
-require 'rspec/core/drb_options'
+RSpec::Support.require_rspec_core "drb_options"
 
 module RSpec
   module Core
diff --git a/lib/rspec/core/formatters.rb b/lib/rspec/core/formatters.rb
index ef6900e3c5..475ad98a36 100644
--- a/lib/rspec/core/formatters.rb
+++ b/lib/rspec/core/formatters.rb
@@ -1,4 +1,4 @@
-require 'rspec/core/formatters/legacy_formatter'
+RSpec::Support.require_rspec_core 'formatters/legacy_formatter'
 
 # ## Built-in Formatters
 #
diff --git a/lib/rspec/core/formatters/base_formatter.rb b/lib/rspec/core/formatters/base_formatter.rb
index e4c3683d69..f1932dc678 100644
--- a/lib/rspec/core/formatters/base_formatter.rb
+++ b/lib/rspec/core/formatters/base_formatter.rb
@@ -1,4 +1,4 @@
-require 'rspec/core/formatters/helpers'
+RSpec::Support.require_rspec_core "formatters/helpers"
 require 'stringio'
 
 module RSpec
diff --git a/lib/rspec/core/formatters/base_text_formatter.rb b/lib/rspec/core/formatters/base_text_formatter.rb
index 398d6b48a7..3b88e5ad3f 100644
--- a/lib/rspec/core/formatters/base_text_formatter.rb
+++ b/lib/rspec/core/formatters/base_text_formatter.rb
@@ -1,4 +1,4 @@
-require 'rspec/core/formatters/base_formatter'
+RSpec::Support.require_rspec_core "formatters/base_formatter"
 require 'set'
 
 module RSpec
diff --git a/lib/rspec/core/formatters/deprecation_formatter.rb b/lib/rspec/core/formatters/deprecation_formatter.rb
index 4f99bcc5c4..693665bc32 100644
--- a/lib/rspec/core/formatters/deprecation_formatter.rb
+++ b/lib/rspec/core/formatters/deprecation_formatter.rb
@@ -1,4 +1,4 @@
-require 'rspec/core/formatters/helpers'
+RSpec::Support.require_rspec_core "formatters/helpers"
 require 'set'
 
 module RSpec
diff --git a/lib/rspec/core/formatters/documentation_formatter.rb b/lib/rspec/core/formatters/documentation_formatter.rb
index d5b2f1b70e..3a27a91fa6 100644
--- a/lib/rspec/core/formatters/documentation_formatter.rb
+++ b/lib/rspec/core/formatters/documentation_formatter.rb
@@ -1,4 +1,4 @@
-require 'rspec/core/formatters/base_text_formatter'
+RSpec::Support.require_rspec_core "formatters/base_text_formatter"
 
 module RSpec
   module Core
diff --git a/lib/rspec/core/formatters/html_formatter.rb b/lib/rspec/core/formatters/html_formatter.rb
index b8092e4e8b..8caed3a030 100644
--- a/lib/rspec/core/formatters/html_formatter.rb
+++ b/lib/rspec/core/formatters/html_formatter.rb
@@ -1,5 +1,5 @@
-require 'rspec/core/formatters/base_text_formatter'
-require 'rspec/core/formatters/html_printer'
+RSpec::Support.require_rspec_core "formatters/base_text_formatter"
+RSpec::Support.require_rspec_core "formatters/html_printer"
 
 module RSpec
   module Core
@@ -134,7 +134,7 @@ def percent_done
         # could output links to images or other files produced during the specs.
         #
         def extra_failure_content(exception)
-          require 'rspec/core/formatters/snippet_extractor'
+          RSpec::Support.require_rspec_core "formatters/snippet_extractor"
           backtrace = exception.backtrace.map {|line| configuration.backtrace_formatter.backtrace_line(line)}
           backtrace.compact!
           @snippet_extractor ||= SnippetExtractor.new
diff --git a/lib/rspec/core/formatters/json_formatter.rb b/lib/rspec/core/formatters/json_formatter.rb
index c862f3d972..8f261054a3 100644
--- a/lib/rspec/core/formatters/json_formatter.rb
+++ b/lib/rspec/core/formatters/json_formatter.rb
@@ -1,4 +1,4 @@
-require 'rspec/core/formatters/base_formatter'
+RSpec::Support.require_rspec_core "formatters/base_formatter"
 require 'json'
 
 module RSpec
diff --git a/lib/rspec/core/formatters/legacy_formatter.rb b/lib/rspec/core/formatters/legacy_formatter.rb
index 9db6c66a58..b4990ef92d 100644
--- a/lib/rspec/core/formatters/legacy_formatter.rb
+++ b/lib/rspec/core/formatters/legacy_formatter.rb
@@ -1,4 +1,4 @@
-require 'rspec/core/formatters/helpers'
+RSpec::Support.require_rspec_core "formatters/helpers"
 require 'stringio'
 
 module RSpec
diff --git a/lib/rspec/core/formatters/progress_formatter.rb b/lib/rspec/core/formatters/progress_formatter.rb
index 9d15f403de..fbe938cdeb 100644
--- a/lib/rspec/core/formatters/progress_formatter.rb
+++ b/lib/rspec/core/formatters/progress_formatter.rb
@@ -1,4 +1,5 @@
-require 'rspec/core/formatters/base_text_formatter'
+RSpec::Support.require_rspec_core "formatters/base_text_formatter"
+
 module RSpec
   module Core
     module Formatters
diff --git a/lib/rspec/core/notifications.rb b/lib/rspec/core/notifications.rb
index 9801751804..b2376e6e5d 100644
--- a/lib/rspec/core/notifications.rb
+++ b/lib/rspec/core/notifications.rb
@@ -1,4 +1,4 @@
-require 'rspec/core/formatters/helpers'
+RSpec::Support.require_rspec_core "formatters/helpers"
 
 module RSpec::Core
   module Notifications
diff --git a/lib/rspec/core/option_parser.rb b/lib/rspec/core/option_parser.rb
index 54dee92133..498a9392c5 100644
--- a/lib/rspec/core/option_parser.rb
+++ b/lib/rspec/core/option_parser.rb
@@ -92,7 +92,7 @@ def parser(options)
         end
 
         parser.on('--init', 'Initialize your project with RSpec.') do |cmd|
-          require 'rspec/core/project_initializer'
+          RSpec::Support.require_rspec_core "project_initializer"
           ProjectInitializer.new.run
           exit
         end
diff --git a/lib/rspec/core/ordering.rb b/lib/rspec/core/ordering.rb
index 7cc27fa43c..4388bf07ec 100644
--- a/lib/rspec/core/ordering.rb
+++ b/lib/rspec/core/ordering.rb
@@ -3,7 +3,7 @@ module Core
     if defined?(::Random)
       RandomNumberGenerator = ::Random
     else
-      require 'rspec/core/backport_random'
+      RSpec::Support.require_rspec_core "backport_random"
       RandomNumberGenerator = RSpec::Core::Backports::Random
     end
 
diff --git a/lib/rspec/core/rake_task.rb b/lib/rspec/core/rake_task.rb
index 649923672d..01e7896a26 100644
--- a/lib/rspec/core/rake_task.rb
+++ b/lib/rspec/core/rake_task.rb
@@ -1,4 +1,6 @@
-require 'rspec/support/warnings'
+require 'rspec/support'
+RSpec::Support.require_rspec_support "warnings"
+
 require 'rake'
 require 'rake/tasklib'
 require 'shellwords'
diff --git a/spec/rspec/core/configuration_spec.rb b/spec/rspec/core/configuration_spec.rb
index 2eba4de1a3..a148361483 100644
--- a/spec/rspec/core/configuration_spec.rb
+++ b/spec/rspec/core/configuration_spec.rb
@@ -109,7 +109,7 @@ def absolute_path_to(dir)
 
     describe "#mock_framework" do
       it "defaults to :rspec" do
-        expect(config).to receive(:require).with('rspec/core/mocking_adapters/rspec')
+        expect(RSpec::Support).to receive(:require_rspec_core).with('mocking_adapters/rspec')
         config.mock_framework
       end
     end
@@ -168,13 +168,13 @@ def absolute_path_to(dir)
       end
 
       it 'uses the named adapter' do
-        expect(config).to receive(:require).with("rspec/core/mocking_adapters/mocha")
+        expect(RSpec::Support).to receive(:require_rspec_core).with('mocking_adapters/mocha')
         stub_const("RSpec::Core::MockingAdapters::Mocha", Module.new)
         config.mock_with :mocha
       end
 
       it "uses the null adapter when given :nothing" do
-        expect(config).to receive(:require).with('rspec/core/mocking_adapters/null').and_call_original
+        expect(RSpec::Support).to receive(:require_rspec_core).with('mocking_adapters/null').and_call_original
         config.mock_with :nothing
       end
 
@@ -191,9 +191,13 @@ def absolute_path_to(dir)
       end
 
       context 'when there are already some example groups defined' do
+        before { allow(RSpec::Support).to receive(:require_rspec_core) }
+
         it 'raises an error since this setting must be applied before any groups are defined' do
           allow(RSpec.world).to receive(:example_groups).and_return([double.as_null_object])
-          stub_const("RSpec::Core::MockingAdapters::Mocha", double(:framework_name => :mocha))
+          mocha = stub_const("RSpec::Core::MockingAdapters::Mocha", Module.new)
+          allow(mocha).to receive_messages(:framework_name => :mocha)
+
           expect {
             config.mock_with :mocha
           }.to raise_error(/must be configured before any example groups are defined/)
@@ -206,7 +210,9 @@ def absolute_path_to(dir)
         end
 
         it 'does not raise an error if re-setting the same config' do
-          stub_const("RSpec::Core::MockingAdapters::Mocha", double(:framework_name => :mocha))
+          mocha = stub_const("RSpec::Core::MockingAdapters::Mocha", Module.new)
+          allow(mocha).to receive_messages(:framework_name => :mocha)
+
           groups = []
           allow(RSpec.world).to receive_messages(:example_groups => groups)
           config.mock_with :mocha