diff --git a/.github/workflows/continuous-integration.yml b/.github/workflows/continuous-integration.yml
index 20bdb8dc..eb9ce9fd 100644
--- a/.github/workflows/continuous-integration.yml
+++ b/.github/workflows/continuous-integration.yml
@@ -6,7 +6,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        ruby: ["2.6", "2.7"]
+        ruby: ["2.6", "2.7", "3.0"]
         db: [sqlite, mysql, postgres]
         exclude:
           - ruby: "2.6"
diff --git a/Dockerfile-2.5 b/Dockerfile-3.0
similarity index 98%
rename from Dockerfile-2.5
rename to Dockerfile-3.0
index f14decab..534d5c92 100644
--- a/Dockerfile-2.5
+++ b/Dockerfile-3.0
@@ -1,4 +1,4 @@
-FROM ruby:2.5
+FROM ruby:3.0
 
 # throw errors if Gemfile has been modified since Gemfile.lock
 RUN bundle config --global frozen 1
diff --git a/Gemfile b/Gemfile
index bc32d458..4c21623c 100644
--- a/Gemfile
+++ b/Gemfile
@@ -20,7 +20,7 @@ gem 'aasm', '~> 5.2.0'
 gem 'acts_as_list'
 gem 'bcrypt', '~> 3.1.16'
 gem 'htmlentities'
-gem 'paperclip'
+gem "kt-paperclip", "~> 6.4", ">= 6.4.1"
 gem 'puma', '~> 5.5'
 gem 'rails_autolink'
 gem 'RedCloth'
diff --git a/Gemfile.lock b/Gemfile.lock
index 4174949a..f1d97d33 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -135,6 +135,12 @@ GEM
       rexml
     kramdown-parser-gfm (1.1.0)
       kramdown (~> 2.0)
+    kt-paperclip (6.4.1)
+      activemodel (>= 4.2.0)
+      activesupport (>= 4.2.0)
+      mime-types
+      mimemagic (~> 0.3.0)
+      terrapin (~> 0.6.0)
     libv8 (3.16.14.19)
     listen (3.7.0)
       rb-fsevent (~> 0.10, >= 0.10.3)
@@ -146,9 +152,9 @@ GEM
       mini_mime (>= 0.1.1)
     marcel (1.0.2)
     method_source (1.0.0)
-    mime-types (3.3.1)
+    mime-types (3.4.1)
       mime-types-data (~> 3.2015)
-    mime-types-data (3.2020.1104)
+    mime-types-data (3.2021.1115)
     mimemagic (0.3.10)
       nokogiri (~> 1)
       rake
@@ -162,12 +168,6 @@ GEM
     nokogiri (1.12.5)
       mini_portile2 (~> 2.6.1)
       racc (~> 1.4)
-    paperclip (6.1.0)
-      activemodel (>= 4.2.0)
-      activesupport (>= 4.2.0)
-      mime-types
-      mimemagic (~> 0.3.0)
-      terrapin (~> 0.6.0)
     parallel (1.21.0)
     parser (3.1.0.0)
       ast (~> 2.4.1)
@@ -336,11 +336,11 @@ DEPENDENCIES
   i18n-tasks (~> 0.9.37)
   jquery-rails (~> 4.4)
   jquery-ui-rails (~> 6.0.1)
+  kt-paperclip (~> 6.4, >= 6.4.1)
   listen
   minitest-stub-const
   mocha
   mysql2 (~> 0.5.3)
-  paperclip
   pg (~> 1.2.3)
   puma (~> 5.5)
   rack-mini-profiler
diff --git a/app/helpers/rendering_helper.rb b/app/helpers/rendering_helper.rb
index ad406aa6..60c6b3c6 100644
--- a/app/helpers/rendering_helper.rb
+++ b/app/helpers/rendering_helper.rb
@@ -13,7 +13,7 @@ module RenderingHelper
         # do not change string; URL is already linked
         href
       else
-        content_tag(:a, h(href), :href => URI.escape(href))
+        content_tag(:a, h(href), :href => href)
       end
     end
   end
diff --git a/app/models/message_gateway.rb b/app/models/message_gateway.rb
index 711e6a92..2a125cd7 100644
--- a/app/models/message_gateway.rb
+++ b/app/models/message_gateway.rb
@@ -26,7 +26,7 @@ class MessageGateway < ActionMailer::Base
     attachment = todo.attachments.build
 
     # create temp file
-    tmp = Tempfile.new(['attachment', '.eml'], { universal_newline: true })
+    tmp = Tempfile.new(['attachment', '.eml'], universal_newline: true)
     tmp.write email.raw_source.gsub(/\r/, "")
 
     # add temp file to attachment. paperclip will copy the file to the right location
diff --git a/app/views/integrations/rest_api.html.erb b/app/views/integrations/rest_api.html.erb
index abf9a758..3d867146 100644
--- a/app/views/integrations/rest_api.html.erb
+++ b/app/views/integrations/rest_api.html.erb
@@ -64,10 +64,10 @@
   <li>/projects/<code><%= t('rest_help.id') %></code>/todos.xml</li>
 </ul>
 
-<p><%= raw t('rest_help.retrieve.limit', {
+<p><%= raw t('rest_help.retrieve.limit',
   fields: '<code>ID, created_at, modified_at, completed_at</code>',
   limit_parameter: '<code>limit_fields</code>',
-  set_to: '<code>index</code>'}) %></p>
+  set_to: '<code>index</code>') %></p>
 
 <pre>
 <code>
@@ -87,10 +87,10 @@
 
 <h2><%= t('rest_help.writing.title') %></h2>
 
-<p><%= raw t('rest_help.writing.description', {
+<p><%= raw t('rest_help.writing.description',
   put: '<code>PUT</code>',
   post: '<code>POST</code>',
-  delete: '<code>DELETE</code>'}) %></p>
+  delete: '<code>DELETE</code>') %></p>
 
 <p><%= t('rest_help.writing.example_title') %></p>
 
@@ -105,9 +105,9 @@ Location: <%= root_url %>projects/65.xml
 </code>
 </pre>
 
-<p><%= raw t('rest_help.writing.example_project_response_title', {
+<p><%= raw t('rest_help.writing.example_project_response_title',
   response_code: '<code>HTTP/1.1 201 Created</code>',
-  header: '<code>Location</code>'}) %></p>
+  header: '<code>Location</code>') %></p>
 
 <pre>
 <code>
@@ -120,9 +120,9 @@ Location: <%= root_url %>todos/452.xml
 </code>
 </pre>
 
-<p><%= raw t('rest_help.writing.example_todo_response_title', {
+<p><%= raw t('rest_help.writing.example_todo_response_title',
   response_code: '<code>HTTP/1.1 201 Created</code>',
-  header: '<code>Location</code>'}) %></p>
+  header: '<code>Location</code>') %></p>
 
 <pre>
 <code>
@@ -143,8 +143,8 @@ Location: <%= root_url %>todos/452.xml
 </code>
 </pre>
 
-<p><%= raw t('rest_help.writing.example_note_response_title', {
-  response_code: '<code>HTTP/1.1 200 OK</code>'}) %></p>
+<p><%= raw t('rest_help.writing.example_note_response_title',
+  response_code: '<code>HTTP/1.1 200 OK</code>') %></p>
 
 <pre>
 <code>
@@ -164,8 +164,8 @@ Location: <%= root_url %>todos/452.xml
 </code>
 </pre>
 
-<p><%= raw t('rest_help.writing.example_delete_title', {
-  delete: '<code>DELETE</code>'}) %></p>
+<p><%= raw t('rest_help.writing.example_delete_title',
+  delete: '<code>DELETE</code>') %></p>
 
 <pre>
 <code>
@@ -176,15 +176,15 @@ Location: <%= root_url %>todos/452.xml
 </code>
 </pre>
 
-<p><%= raw t('rest_help.writing.example_delete_response_title', {
-  response_code: '<code>HTTP/1.1 200 OK</code>'}) %></p>
+<p><%= raw t('rest_help.writing.example_delete_response_title',
+  response_code: '<code>HTTP/1.1 200 OK</code>') %></p>
 
 <h2><%= t('rest_help.response.title') %></h2>
 
-<p><%= raw t('rest_help.response.description', {
+<p><%= raw t('rest_help.response.description',
   response_200: '<code>200 OK</code>',
   response_201: '<code>201 Created</code>',
-  example_call: '<code>GET /contexts/2/todos.xml</code>'}) %></p>
+  example_call: '<code>GET /contexts/2/todos.xml</code>') %></p>
 
 <p><%= t('rest_help.response.xml_description') %></p>
 
@@ -200,11 +200,11 @@ $ curl -u username:p4ssw0rd -H "Content-Type: text/xml" \
 
 <h2><%= t('rest_help.activeresource.title') %></h2>
 
-<p><%= raw I18n.t 'rest_help.activeresource.description', {
+<p><%= raw I18n.t 'rest_help.activeresource.description',
   activeresource_link: link_to(I18n.t('rest_help.activeresource.activeresource_link_text'), 'http://weblog.rubyonrails.org/2007/9/30/rails-2-0-0-preview-release'),
   ror_link: link_to(I18n.t('rest_help.activeresource.ror_link_text'), 'http://www.rubyonrails.org'),
   gem_command: '<code>gem install activeresource --source http://gems.rubyonrails.org --include-dependencies</code>'
-} %></p>
+%></p>
 
 <pre>
 <code>
@@ -226,8 +226,8 @@ Loading development environment (Rails 1.2.4)
 </code>
 </pre>
 
-<p><%= raw I18n.t 'rest_help.activeresource.wrapper_description', {
-  signals_link: link_to(I18n.t('rest_help.activeresource.signals_link_text'), 'http://www.37signals.com')} %></p>
+<p><%= raw I18n.t 'rest_help.activeresource.wrapper_description',
+  signals_link: link_to(I18n.t('rest_help.activeresource.signals_link_text'), 'http://www.37signals.com') %></p>
 
 <pre>
 <code>
@@ -246,13 +246,13 @@ irb(main):003:0&gt;
 <p><%= t('rest_help.notes.description') %></p>
 
 <ul>
-  <li><%= raw I18n.t 'rest_help.notes.bullet1', {
+  <li><%= raw I18n.t 'rest_help.notes.bullet1',
     id: '<code>ID</code>',
-    url: '<span class="caps">URL</span>'} %></li>
-  <li><%= raw I18n.t 'rest_help.notes.bullet2', {
-    omit: '<code>...</code>' } %></li>
+    url: '<span class="caps">URL</span>' %></li>
+  <li><%= raw I18n.t 'rest_help.notes.bullet2',
+    omit: '<code>...</code>' %></li>
 </ul>
 
-<p><%= raw I18n.t 'rest_help.notes.curl_description', {
-  curl: link_to(I18n.t('rest_help.curl_link_text'), 'http://en.wikipedia.org/wiki/CURL')} %></p>
+<p><%= raw I18n.t 'rest_help.notes.curl_description',
+  curl: link_to(I18n.t('rest_help.curl_link_text'), 'http://en.wikipedia.org/wiki/CURL') %></p>
 </div>
diff --git a/doc/CHANGELOG.md b/doc/CHANGELOG.md
index ab3a3778..5d788103 100644
--- a/doc/CHANGELOG.md
+++ b/doc/CHANGELOG.md
@@ -2,6 +2,10 @@ See doc/upgrading.md for the upgrade documentation!
 
 ## Version 2.6
 
+## New features
+
+* Ruby 3.0 is now supported.
+
 ## Removed features
 
 * No longer supporting EOL Ruby 2.5
diff --git a/test-envs/docker-compose-2.5-mysql.yml b/test-envs/docker-compose-3.0-mysql.yml
similarity index 95%
rename from test-envs/docker-compose-2.5-mysql.yml
rename to test-envs/docker-compose-3.0-mysql.yml
index 249e1f35..2cd0413f 100644
--- a/test-envs/docker-compose-2.5-mysql.yml
+++ b/test-envs/docker-compose-3.0-mysql.yml
@@ -10,7 +10,7 @@ services:
   web:
     build:
       context: ..
-      dockerfile: Dockerfile-2.5
+      dockerfile: Dockerfile-3.0
     environment:
       # These are set in script/ci-build, so we need to pass-thru them.
       RAILS_ENV: $RAILS_ENV
diff --git a/test-envs/docker-compose-3.0-postgres.yml b/test-envs/docker-compose-3.0-postgres.yml
new file mode 100644
index 00000000..0c6d9b03
--- /dev/null
+++ b/test-envs/docker-compose-3.0-postgres.yml
@@ -0,0 +1,32 @@
+version: '3'
+services:
+  db:
+    image: postgres:13
+    environment:
+      POSTGRES_DB: ${DATABASE_NAME:-tracks}
+      POSTGRES_PASSWORD: password
+    volumes:
+      - db-data:/var/lib/postgresql/data
+  web:
+    build:
+      context: ..
+      dockerfile: Dockerfile-3.0
+    environment:
+      # These are set in script/ci-build, so we need to pass-thru them.
+      RAILS_ENV: $RAILS_ENV
+      DATABASE_NAME: $DATABASE_NAME
+      DATABASE_USERNAME: postgres
+      DATABASE_PASSWORD: password
+      DATABASE_TYPE: postgresql
+      DATABASE_ENCODING: unicode
+      DATABASE_PORT: 5432
+    volumes:
+      - ${VOLUME:-..}:/app:Z
+      - ${VOLUME:-..}/config/database.docker.yml:/app/config/database.yml:Z
+      - ${VOLUME:-..}/config/site.docker.yml:/app/config/site.yml:Z
+    ports:
+      - 3000:3000
+    depends_on:
+      - db
+volumes:
+  db-data:
diff --git a/test-envs/docker-compose-3.0-sqlite.yml b/test-envs/docker-compose-3.0-sqlite.yml
new file mode 100644
index 00000000..ba4d3709
--- /dev/null
+++ b/test-envs/docker-compose-3.0-sqlite.yml
@@ -0,0 +1,17 @@
+version: '3'
+services:
+  web:
+    build:
+      context: ..
+      dockerfile: Dockerfile-3.0
+    environment:
+      # These are set in script/ci-build, so we need to pass-thru them.
+      RAILS_ENV: $RAILS_ENV
+      DATABASE_NAME: "/app/db.sqlite"
+      DATABASE_TYPE: sqlite3
+    volumes:
+      - ${VOLUME:-..}:/app:Z
+      - ${VOLUME:-..}/config/database.docker.yml:/app/config/database.yml:Z
+      - ${VOLUME:-..}/config/site.docker.yml:/app/config/site.yml:Z
+    ports:
+      - 3000:3000
diff --git a/test/helpers/rendering_helper_test.rb b/test/helpers/rendering_helper_test.rb
index 8aae34e9..14740710 100644
--- a/test/helpers/rendering_helper_test.rb
+++ b/test/helpers/rendering_helper_test.rb
@@ -28,7 +28,7 @@ class RenderingHelperTest < ActionView::TestCase
   end
 
   test "message link" do
-    expected = '<p>Call <a href="message://%3C123%3E">message://&lt;123&gt;</a>.</p>'
+    expected = '<p>Call <a href="message://<123>">message://&lt;123&gt;</a>.</p>'
     actual = render_text("Call message://<123>.")
     assert_equal(expected, actual)
   end