diff --git a/Gemfile b/Gemfile
index 63b7713395..8c718b3569 100644
--- a/Gemfile
+++ b/Gemfile
@@ -160,3 +160,5 @@ gem 'cocoon', '~> 1.2'
 
 gem 'net-http', '~> 0.3.2'
 gem 'rubyzip', '~> 2.3'
+
+gem 'hcaptcha', '~> 7.1'
diff --git a/Gemfile.lock b/Gemfile.lock
index 20cb29355d..b5d277097a 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -312,6 +312,8 @@ GEM
       sysexits (~> 1.1)
     hashdiff (1.0.1)
     hashie (5.0.0)
+    hcaptcha (7.1.0)
+      json
     highline (2.1.0)
     hiredis (0.6.3)
     hkdf (0.3.0)
@@ -806,6 +808,7 @@ DEPENDENCIES
   fuubar (~> 2.5)
   haml-rails (~> 2.0)
   haml_lint
+  hcaptcha (~> 7.1)
   hiredis (~> 0.6)
   htmlentities (~> 4.3)
   http (~> 5.1)
diff --git a/app/controllers/auth/confirmations_controller.rb b/app/controllers/auth/confirmations_controller.rb
index 010fd37556..c57eb946e1 100644
--- a/app/controllers/auth/confirmations_controller.rb
+++ b/app/controllers/auth/confirmations_controller.rb
@@ -1,21 +1,63 @@
 # frozen_string_literal: true
 
 class Auth::ConfirmationsController < Devise::ConfirmationsController
+  include CaptchaConcern
+
   layout 'auth'
 
   before_action :set_body_classes
+  before_action :set_confirmation_user!, only: [:show, :confirm_captcha]
   before_action :require_unconfirmed!
 
+  before_action :extend_csp_for_captcha!, only: [:show, :confirm_captcha]
+  before_action :require_captcha_if_needed!, only: [:show]
+
   skip_before_action :require_functional!
 
+  def show
+    old_session_values = session.to_hash
+    reset_session
+    session.update old_session_values.except('session_id')
+
+    super
+  end
+
   def new
     super
 
     resource.email = current_user.unconfirmed_email || current_user.email if user_signed_in?
   end
 
+  def confirm_captcha
+    check_captcha! do |message|
+      flash.now[:alert] = message
+      render :captcha
+      return
+    end
+
+    show
+  end
+
   private
 
+  def require_captcha_if_needed!
+    render :captcha if captcha_required?
+  end
+
+  def set_confirmation_user!
+    # We need to reimplement looking up the user because
+    # Devise::ConfirmationsController#show looks up and confirms in one
+    # step.
+    confirmation_token = params[:confirmation_token]
+    return if confirmation_token.nil?
+
+    @confirmation_user = User.find_first_by_auth_conditions(confirmation_token: confirmation_token)
+  end
+
+  def captcha_user_bypass?
+    return true if @confirmation_user.nil? || @confirmation_user.confirmed?
+  end
+
   def require_unconfirmed!
     if user_signed_in? && current_user.confirmed? && current_user.unconfirmed_email.blank?
       redirect_to(current_user.approved? ? root_path : edit_user_registration_path)
diff --git a/app/controllers/concerns/captcha_concern.rb b/app/controllers/concerns/captcha_concern.rb
new file mode 100644
index 0000000000..538c1ffb14
--- /dev/null
+++ b/app/controllers/concerns/captcha_concern.rb
@@ -0,0 +1,59 @@
+# frozen_string_literal: true
+
+module CaptchaConcern
+  extend ActiveSupport::Concern
+  include Hcaptcha::Adapters::ViewMethods
+
+  included do
+    helper_method :render_captcha
+  end
+
+  def captcha_available?
+    ENV['HCAPTCHA_SECRET_KEY'].present? && ENV['HCAPTCHA_SITE_KEY'].present?
+  end
+
+  def captcha_enabled?
+    captcha_available? && Setting.captcha_enabled
+  end
+
+  def captcha_user_bypass?
+    false
+  end
+
+  def captcha_required?
+    captcha_enabled? && !captcha_user_bypass?
+  end
+
+  def check_captcha!
+    return true unless captcha_required?
+
+    if verify_hcaptcha
+      true
+    else
+      if block_given?
+        message = flash[:hcaptcha_error]
+        flash.delete(:hcaptcha_error)
+        yield message
+      end
+      false
+    end
+  end
+
+  def extend_csp_for_captcha!
+    policy = request.content_security_policy
+    return unless captcha_required? && policy.present?
+
+    %w(script_src frame_src style_src connect_src).each do |directive|
+      values = policy.send(directive)
+      values << 'https://hcaptcha.com' unless values.include?('https://hcaptcha.com') || values.include?('https:')
+      values << 'https://*.hcaptcha.com' unless values.include?('https://*.hcaptcha.com') || values.include?('https:')
+      policy.send(directive, *values)
+    end
+  end
+
+  def render_captcha
+    return unless captcha_required?
+
+    hcaptcha_tags
+  end
+end
diff --git a/app/helpers/admin/settings_helper.rb b/app/helpers/admin/settings_helper.rb
index a133b4e7d9..552a3ee5a8 100644
--- a/app/helpers/admin/settings_helper.rb
+++ b/app/helpers/admin/settings_helper.rb
@@ -1,4 +1,7 @@
 # frozen_string_literal: true
 
 module Admin::SettingsHelper
+  def captcha_available?
+    ENV['HCAPTCHA_SECRET_KEY'].present? && ENV['HCAPTCHA_SITE_KEY'].present?
+  end
 end
diff --git a/app/javascript/styles/mastodon/forms.scss b/app/javascript/styles/mastodon/forms.scss
index 03e06c1000..57f077c4e8 100644
--- a/app/javascript/styles/mastodon/forms.scss
+++ b/app/javascript/styles/mastodon/forms.scss
@@ -136,6 +136,10 @@ code {
     line-height: 22px;
     color: $secondary-text-color;
     margin-bottom: 30px;
+
+    a {
+      color: $highlight-text-color;
+    }
   }
 
   .rules-list {
@@ -1039,6 +1043,10 @@ code {
   }
 }
 
+.simple_form .h-captcha {
+  text-align: center;
+}
+
 .permissions-list {
   &__item {
     padding: 15px;
diff --git a/app/models/form/admin_settings.rb b/app/models/form/admin_settings.rb
index de965cb0ba..a6be55fd7b 100644
--- a/app/models/form/admin_settings.rb
+++ b/app/models/form/admin_settings.rb
@@ -33,6 +33,7 @@ class Form::AdminSettings
     content_cache_retention_period
     backups_retention_period
     status_page_url
+    captcha_enabled
   ).freeze
 
   INTEGER_KEYS = %i(
@@ -52,6 +53,7 @@ class Form::AdminSettings
     trendable_by_default
     noindex
     require_invite_text
+    captcha_enabled
   ).freeze
 
   UPLOAD_KEYS = %i(
diff --git a/app/views/admin/settings/registrations/show.html.haml b/app/views/admin/settings/registrations/show.html.haml
index 0db9f3536f..84492a08a1 100644
--- a/app/views/admin/settings/registrations/show.html.haml
+++ b/app/views/admin/settings/registrations/show.html.haml
@@ -20,6 +20,10 @@
     .fields-row__column.fields-row__column-6.fields-group
       = f.input :require_invite_text, as: :boolean, wrapper: :with_label, disabled: !approved_registrations?
 
+  - if captcha_available?
+    .fields-group
+      = f.input :captcha_enabled, as: :boolean, wrapper: :with_label, label: t('admin.settings.captcha_enabled.title'), hint: t('admin.settings.captcha_enabled.desc_html')
+
   .fields-group
     = f.input :closed_registrations_message, as: :text, wrapper: :with_block_label, input_html: { rows: 2 }
 
diff --git a/app/views/auth/confirmations/captcha.html.haml b/app/views/auth/confirmations/captcha.html.haml
new file mode 100644
index 0000000000..1f577383eb
--- /dev/null
+++ b/app/views/auth/confirmations/captcha.html.haml
@@ -0,0 +1,15 @@
+- content_for :page_title do
+  = t('auth.captcha_confirmation.title')
+
+= form_tag auth_captcha_confirmation_url, method: 'POST', class: 'simple_form' do
+  = render 'auth/shared/progress', stage: 'confirm'
+
+  = hidden_field_tag :confirmation_token, params[:confirmation_token]
+
+  %p.lead= t('auth.captcha_confirmation.hint_html')
+
+  .field-group
+    = render_captcha
+
+  .actions
+    %button.button= t('challenge.confirm')
diff --git a/config/locales/en.yml b/config/locales/en.yml
index 29abec9437..aea9656602 100644
--- a/config/locales/en.yml
+++ b/config/locales/en.yml
@@ -731,6 +731,9 @@ en:
       branding:
         preamble: Your server's branding differentiates it from other servers in the network. This information may be displayed across a variety of environments, such as Mastodon's web interface, native applications, in link previews on other websites and within messaging apps, and so on. For this reason, it is best to keep this information clear, short and concise.
         title: Branding
+      captcha_enabled:
+        desc_html: This relies on external scripts from hCaptcha, which may be a security and privacy concern. In addition, <strong>this can make the registration process significantly less accessible to some (especially disabled) people</strong>. For these reasons, please consider alternative measures such as approval-based or invite-based registration.
+        title: Require new users to solve a CAPTCHA to confirm their account
       content_retention:
         preamble: Control how user-generated content is stored in Mastodon.
         title: Content retention
@@ -979,6 +982,9 @@ en:
     your_token: Your access token
   auth:
     apply_for_account: Request an account
+    captcha_confirmation:
+      hint_html: Just one more step! To confirm your account, this server requires you to solve a CAPTCHA. You can <a href="/about/more">contact the server administrator</a> if you have questions or need assistance with confirming your account.
+      title: User verification
     change_password: Password
     confirmations:
       wrong_email_hint: If that e-mail address is not correct, you can change it in account settings.
diff --git a/config/routes.rb b/config/routes.rb
index 04d5ec2a65..45b3d90e0b 100644
--- a/config/routes.rb
+++ b/config/routes.rb
@@ -71,6 +71,7 @@ Rails.application.routes.draw do
       resource :setup, only: [:show, :update], controller: :setup
       resource :challenge, only: [:create], controller: :challenges
       get 'sessions/security_key_options', to: 'sessions#webauthn_options'
+      post 'captcha_confirmation', to: 'confirmations#confirm_captcha', as: :captcha_confirmation
     end
   end
 
diff --git a/config/settings.yml b/config/settings.yml
index 4ac521a4b0..67297c26ce 100644
--- a/config/settings.yml
+++ b/config/settings.yml
@@ -37,6 +37,7 @@ defaults: &defaults
   show_domain_blocks_rationale: 'disabled'
   require_invite_text: false
   backups_retention_period: 7
+  captcha_enabled: false
 
 development:
   <<: *defaults