diff --git a/lib/bundler.rb b/lib/bundler.rb
index f4f9891247a7c6..668c0b66607bb5 100644
--- a/lib/bundler.rb
+++ b/lib/bundler.rb
@@ -40,6 +40,7 @@ module Bundler
   SUDO_MUTEX = Thread::Mutex.new
 
   autoload :Checksum,               File.expand_path("bundler/checksum", __dir__)
+  autoload :CIDetector,             File.expand_path("bundler/ci_detector", __dir__)
   autoload :Definition,             File.expand_path("bundler/definition", __dir__)
   autoload :Dependency,             File.expand_path("bundler/dependency", __dir__)
   autoload :Deprecate,              File.expand_path("bundler/deprecate", __dir__)
diff --git a/lib/bundler/ci_detector.rb b/lib/bundler/ci_detector.rb
new file mode 100644
index 00000000000000..e5fedbdea8d383
--- /dev/null
+++ b/lib/bundler/ci_detector.rb
@@ -0,0 +1,75 @@
+# frozen_string_literal: true
+
+module Bundler
+  module CIDetector
+    # NOTE: Any changes made here will need to be made to both lib/rubygems/ci_detector.rb and
+    # bundler/lib/bundler/ci_detector.rb (which are enforced duplicates).
+    # TODO: Drop that duplication once bundler drops support for RubyGems 3.4
+    #
+    # ## Recognized CI providers, their signifiers, and the relevant docs ##
+    #
+    # Travis CI   - CI, TRAVIS            https://docs.travis-ci.com/user/environment-variables/#default-environment-variables
+    # Cirrus CI   - CI, CIRRUS_CI         https://cirrus-ci.org/guide/writing-tasks/#environment-variables
+    # Circle CI   - CI, CIRCLECI          https://circleci.com/docs/variables/#built-in-environment-variables
+    # Gitlab CI   - CI, GITLAB_CI         https://docs.gitlab.com/ee/ci/variables/
+    # AppVeyor    - CI, APPVEYOR          https://www.appveyor.com/docs/environment-variables/
+    # CodeShip    - CI_NAME               https://docs.cloudbees.com/docs/cloudbees-codeship/latest/pro-builds-and-configuration/environment-variables#_default_environment_variables
+    # dsari       - CI, DSARI             https://github.com/rfinnie/dsari#running
+    # Jenkins     - BUILD_NUMBER          https://www.jenkins.io/doc/book/pipeline/jenkinsfile/#using-environment-variables
+    # TeamCity    - TEAMCITY_VERSION      https://www.jetbrains.com/help/teamcity/predefined-build-parameters.html#Predefined+Server+Build+Parameters
+    # Appflow     - CI_BUILD_ID           https://ionic.io/docs/appflow/automation/environments#predefined-environments
+    # TaskCluster - TASKCLUSTER_ROOT_URL  https://docs.taskcluster.net/docs/manual/design/env-vars
+    # Semaphore   - CI, SEMAPHORE         https://docs.semaphoreci.com/ci-cd-environment/environment-variables/
+    # BuildKite   - CI, BUILDKITE         https://buildkite.com/docs/pipelines/environment-variables
+    # GoCD        - GO_SERVER_URL         https://docs.gocd.org/current/faq/dev_use_current_revision_in_build.html
+    # GH Actions  - CI, GITHUB_ACTIONS    https://docs.github.com/en/actions/learn-github-actions/variables#default-environment-variables
+    #
+    # ### Some "standard" ENVs that multiple providers may set ###
+    #
+    # * CI - this is set by _most_ (but not all) CI providers now; it's approaching a standard.
+    # * CI_NAME - Not as frequently used, but some providers set this to specify their own name
+
+    # Any of these being set is a reasonably reliable indicator that we are
+    # executing in a CI environment.
+    ENV_INDICATORS = [
+      "CI",
+      "CI_NAME",
+      "CONTINUOUS_INTEGRATION",
+      "BUILD_NUMBER",
+      "CI_APP_ID",
+      "CI_BUILD_ID",
+      "CI_BUILD_NUMBER",
+      "RUN_ID",
+      "TASKCLUSTER_ROOT_URL",
+    ].freeze
+
+    # For each CI, this env suffices to indicate that we're on _that_ CI's
+    # containers. (A few of them only supply a CI_NAME variable, which is also
+    # nice). And if they set "CI" but we can't tell which one they are, we also
+    # want to know that - a bare "ci" without another token tells us as much.
+    ENV_DESCRIPTORS = {
+      "TRAVIS" => "travis",
+      "CIRCLECI" => "circle",
+      "CIRRUS_CI" => "cirrus",
+      "DSARI" => "dsari",
+      "SEMAPHORE" => "semaphore",
+      "JENKINS_URL" => "jenkins",
+      "BUILDKITE" => "buildkite",
+      "GO_SERVER_URL" => "go",
+      "GITLAB_CI" => "gitlab",
+      "GITHUB_ACTIONS" => "github",
+      "TASKCLUSTER_ROOT_URL" => "taskcluster",
+      "CI" => "ci",
+    }.freeze
+
+    def self.ci?
+      ENV_INDICATORS.any? {|var| ENV.include?(var) }
+    end
+
+    def self.ci_strings
+      matching_names = ENV_DESCRIPTORS.select {|env, _| ENV[env] }.values
+      matching_names << ENV["CI_NAME"].downcase if ENV["CI_NAME"]
+      matching_names.reject(&:empty?).sort.uniq
+    end
+  end
+end
diff --git a/spec/bundler/bundler/ci_detector_spec.rb b/spec/bundler/bundler/ci_detector_spec.rb
new file mode 100644
index 00000000000000..299d8005e8febc
--- /dev/null
+++ b/spec/bundler/bundler/ci_detector_spec.rb
@@ -0,0 +1,21 @@
+# frozen_string_literal: true
+
+RSpec.describe Bundler::CIDetector do
+  # This is properly tested in rubygems, under the name Gem::CIDetector
+  # But the test that confirms that our version _stays in sync_ with that version
+  # will live here.
+
+  it "stays in sync with the rubygems implementation" do
+    rubygems_implementation_path = File.join(git_root, "lib", "rubygems", "ci_detector.rb")
+    expect(File.exist?(rubygems_implementation_path)).to be_truthy
+    rubygems_code = File.read(rubygems_implementation_path)
+    denamespaced_rubygems_code = rubygems_code.sub("Gem", "NAMESPACE")
+
+    bundler_implementation_path = File.join(source_lib_dir, "bundler", "ci_detector.rb")
+    expect(File.exist?(bundler_implementation_path)).to be_truthy
+    bundler_code = File.read(bundler_implementation_path)
+    denamespaced_bundler_code = bundler_code.sub("Bundler", "NAMESPACE")
+
+    expect(denamespaced_bundler_code).to eq(denamespaced_rubygems_code)
+  end
+end