diff --git a/.rubocop.yml b/.rubocop.yml
index af922f52..f9117f32 100644
--- a/.rubocop.yml
+++ b/.rubocop.yml
@@ -13,6 +13,7 @@ AllCops:
     # Other
     - 'test/benchmarks/**/*'
     - 'test/profilers/**/*'
+  TargetRubyVersion: 2.6
 
 # I often use @_variable to avoid clashing.
 Naming/MemoizedInstanceVariableName:
diff --git a/.rubocop_opinionated.yml b/.rubocop_opinionated.yml
index 761e2c7d..a9bc89bc 100644
--- a/.rubocop_opinionated.yml
+++ b/.rubocop_opinionated.yml
@@ -15,12 +15,6 @@ Layout/LineLength:
     - 'test/**/*_test.rb'
   Max: 100
 
-Lint/ConstantDefinitionInBlock:
-  Exclude:
-    - 'Rakefile'
-    - 'spec/**/*'
-    - 'test/**/*'
-
 # [codesmell]
 Metrics/AbcSize:
   Enabled: false
@@ -101,12 +95,6 @@ Layout/EmptyLinesAroundModuleBody:
 Layout/EmptyLineBetweenDefs:
   Enabled: false
 
-# I personally don't care about the format style.
-# In most cases I like to use %, but not at the point I want to enforce it
-# as a convention in the entire code.
-Style/FormatString:
-  Enabled: false
-
 # Annotated tokens (like %<foo>s) are a good thing, but in most cases we don't need them.
 # %s is a simpler and straightforward version that works in almost all cases. So don't complain.
 Style/FormatStringToken:
@@ -116,11 +104,6 @@ Style/FormatStringToken:
 Style/NegatedIf:
   Enabled: false
 
-# For years, %w() has been the de-facto standard. A lot of libraries are using ().
-# Switching to [] would be a nightmare.
-Style/PercentLiteralDelimiters:
-  Enabled: false
-
 # There are cases were the inline rescue is ok. We can either downgrade the severity,
 # or rely on the developer judgement on a case-by-case basis.
 Style/RescueModifier:
@@ -129,17 +112,6 @@ Style/RescueModifier:
 Style/SymbolArray:
   EnforcedStyle: brackets
 
-# Sorry, but using trailing spaces helps readability.
-#
-#   %w( foo bar )
-#
-# looks better to me than
-#
-#   %w( foo bar )
-#
-Layout/SpaceInsidePercentLiteralDelimiters:
-  Enabled: false
-
 # Hate It or Love It, I prefer double quotes as this is more consistent
 # with several other programming languages and the output of puts and inspect.
 Style/StringLiterals:
diff --git a/CHANGELOG.md b/CHANGELOG.md
index b6178f56..8b1729f0 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -3,6 +3,13 @@
 This project uses [Semantic Versioning 2.0.0](https://semver.org/).
 
 
+## main
+
+### Changed
+
+- Minimum Ruby version is 2.6
+
+
 ## 4.0.7
 
 ### Fixes
diff --git a/Gemfile b/Gemfile
index 8c679696..b41c6f2e 100644
--- a/Gemfile
+++ b/Gemfile
@@ -10,5 +10,5 @@ gem "memory_profiler", require: false
 gem "minitest"
 gem "minitest-reporters"
 gem "mocha"
-gem "rubocop", "~>0.90", require: false
+gem "rubocop", require: false
 gem "yard"
diff --git a/README.md b/README.md
index 0747354f..4cf31e3a 100644
--- a/README.md
+++ b/README.md
@@ -16,7 +16,7 @@
 
 ## Requirements
 
-<tt>PublicSuffix</tt> requires **Ruby >= 2.3**. For an older versions of Ruby use a previous release.
+<tt>PublicSuffix</tt> requires **Ruby >= 2.6**. For an older versions of Ruby use a previous release.
 
 
 ## Installation
diff --git a/Rakefile b/Rakefile
index 26a6c994..59b3b3b7 100644
--- a/Rakefile
+++ b/Rakefile
@@ -9,7 +9,7 @@ task default: [:test, :rubocop]
 require "rake/testtask"
 
 Rake::TestTask.new do |t|
-  t.libs = %w( lib test )
+  t.libs = %w[lib test]
   t.pattern = "test/**/*_test.rb"
   t.verbose = !ENV["VERBOSE"].nil?
   t.warning = !ENV["WARNING"].nil?
@@ -42,10 +42,10 @@ desc "Downloads the Public Suffix List file from the repository and stores it lo
 task :"update-list" do
   require "net/http"
 
-  DEFINITION_URL = "https://raw.githubusercontent.com/publicsuffix/list/master/public_suffix_list.dat"
+  definition_url = "https://raw.githubusercontent.com/publicsuffix/list/master/public_suffix_list.dat"
 
   File.open("data/list.txt", "w+") do |f|
-    response = Net::HTTP.get_response(URI.parse(DEFINITION_URL))
+    response = Net::HTTP.get_response(URI.parse(definition_url))
     response.body
     f.write(response.body)
   end
diff --git a/lib/public_suffix.rb b/lib/public_suffix.rb
index c0f3fab6..a4ed1403 100644
--- a/lib/public_suffix.rb
+++ b/lib/public_suffix.rb
@@ -169,7 +169,7 @@ def self.normalize(name)
 
     return DomainInvalid.new("Name is blank") if name.empty?
     return DomainInvalid.new("Name starts with a dot") if name.start_with?(DOT)
-    return DomainInvalid.new("%s is not expected to contain a scheme" % name) if name.include?("://")
+    return DomainInvalid.new(format("%s is not expected to contain a scheme", name)) if name.include?("://")
 
     name
   end
diff --git a/lib/public_suffix/rule.rb b/lib/public_suffix/rule.rb
index d41a4807..c89304e6 100644
--- a/lib/public_suffix/rule.rb
+++ b/lib/public_suffix/rule.rb
@@ -221,7 +221,7 @@ class Wildcard < Base
       # @param  content [String] the content of the rule
       # @param  private [Boolean]
       def self.build(content, private: false)
-        new(value: content.to_s[2..-1], private: private)
+        new(value: content.to_s[2..], private: private)
       end
 
       # Initializes a new rule.
@@ -269,7 +269,7 @@ class Exception < Base
       # @param  content [#to_s] the content of the rule
       # @param  private [Boolean]
       def self.build(content, private: false)
-        new(value: content.to_s[1..-1], private: private)
+        new(value: content.to_s[1..], private: private)
       end
 
       # Gets the original rule definition.
@@ -299,7 +299,7 @@ def decompose(domain)
       #
       # @return [Array<String>]
       def parts
-        @value.split(DOT)[1..-1]
+        @value.split(DOT)[1..]
       end
 
     end
diff --git a/public_suffix.gemspec b/public_suffix.gemspec
index ae552fc9..cbf035c1 100644
--- a/public_suffix.gemspec
+++ b/public_suffix.gemspec
@@ -20,7 +20,7 @@ Gem::Specification.new do |s|
     "source_code_uri" => "https://github.com/weppos/publicsuffix-ruby/tree/v#{s.version}",
   }
 
-  s.required_ruby_version = ">= 2.3"
+  s.required_ruby_version = ">= 2.6"
 
   s.require_paths    = ["lib"]
   s.files            = `git ls-files`.split("\n")
diff --git a/test/acceptance_test.rb b/test/acceptance_test.rb
index 371bfe13..6e114f45 100644
--- a/test/acceptance_test.rb
+++ b/test/acceptance_test.rb
@@ -64,7 +64,7 @@ def test_invalid
   def test_rejected
     REJECTED_CASES.each do |name, expected|
       assert_equal expected, PublicSuffix.valid?(name),
-                   "Expected %s to be %s" % [name.inspect, expected.inspect]
+                   format("Expected %s to be %s", name.inspect, expected.inspect)
       assert !valid_domain?(name),
              "#{name} expected to be invalid"
     end
@@ -72,9 +72,9 @@ def test_rejected
 
 
   CASE_CASES = [
-    ["Www.google.com", %w( www google com )],
-    ["www.Google.com", %w( www google com )],
-    ["www.google.Com", %w( www google com )],
+    ["Www.google.com", %w[www google com]],
+    ["www.Google.com", %w[www google com]],
+    ["www.google.Com", %w[www google com]],
   ].freeze
 
   def test_ignore_case
diff --git a/test/psl_test.rb b/test/psl_test.rb
index fae398f7..919029b4 100644
--- a/test/psl_test.rb
+++ b/test/psl_test.rb
@@ -45,7 +45,7 @@ def test_valid
     end
 
     message = "The following #{failures.size} tests fail:\n"
-    failures.each { |i, o, d| message += "Expected %s to be %s, got %s\n" % [i.inspect, o.inspect, d.inspect] }
+    failures.each { |i, o, d| message += format("Expected %s to be %s, got %s\n", i.inspect, o.inspect, d.inspect) }
     assert_equal 0, failures.size, message
   end
 
diff --git a/test/unit/domain_test.rb b/test/unit/domain_test.rb
index 968462d9..f3ae4bed 100644
--- a/test/unit/domain_test.rb
+++ b/test/unit/domain_test.rb
@@ -10,15 +10,15 @@ def setup
 
   # Tokenizes given input into labels.
   def test_self_name_to_labels
-    assert_equal  %w( someone spaces live com ),
+    assert_equal  %w[someone spaces live com],
                   PublicSuffix::Domain.name_to_labels("someone.spaces.live.com")
-    assert_equal  %w( leontina23samiko wiki zoho com ),
+    assert_equal  %w[leontina23samiko wiki zoho com],
                   PublicSuffix::Domain.name_to_labels("leontina23samiko.wiki.zoho.com")
   end
 
   # Converts input into String.
   def test_self_name_to_labels_converts_input_to_string
-    assert_equal  %w( someone spaces live com ),
+    assert_equal  %w[someone spaces live com],
                   PublicSuffix::Domain.name_to_labels(:"someone.spaces.live.com")
   end
 
diff --git a/test/unit/list_test.rb b/test/unit/list_test.rb
index 98529352..3b0160e5 100644
--- a/test/unit/list_test.rb
+++ b/test/unit/list_test.rb
@@ -214,7 +214,7 @@ def test_self_parse
     assert_instance_of PublicSuffix::List, list
     assert_equal 4, list.size
 
-    rules = %w( com *.uk !british-library.uk blogspot.com ).map { |name| PublicSuffix::Rule.factory(name) }
+    rules = %w[com *.uk !british-library.uk blogspot.com].map { |name| PublicSuffix::Rule.factory(name) }
     assert_equal rules, list.each.to_a
 
     # private domains
diff --git a/test/unit/rule_test.rb b/test/unit/rule_test.rb
index d1cc6094..81d4522e 100644
--- a/test/unit/rule_test.rb
+++ b/test/unit/rule_test.rb
@@ -29,8 +29,8 @@ def test_factory_should_return_rule_wildcard
   def test_default_returns_default_wildcard
     default = PublicSuffix::Rule.default
     assert_equal PublicSuffix::Rule::Wildcard.build("*"), default
-    assert_equal %w( example tldnotlisted ), default.decompose("example.tldnotlisted")
-    assert_equal %w( www.example tldnotlisted ), default.decompose("www.example.tldnotlisted")
+    assert_equal %w[example tldnotlisted], default.decompose("example.tldnotlisted")
+    assert_equal %w[www.example tldnotlisted], default.decompose("www.example.tldnotlisted")
   end
 
 end
@@ -140,15 +140,15 @@ def test_length
   end
 
   def test_parts
-    assert_equal %w(com), @klass.build("com").parts
-    assert_equal %w(co com), @klass.build("co.com").parts
-    assert_equal %w(mx co com), @klass.build("mx.co.com").parts
+    assert_equal %w[com], @klass.build("com").parts
+    assert_equal %w[co com], @klass.build("co.com").parts
+    assert_equal %w[mx co com], @klass.build("mx.co.com").parts
   end
 
   def test_decompose
     assert_equal [nil, nil], @klass.build("com").decompose("com")
-    assert_equal %w( example com ), @klass.build("com").decompose("example.com")
-    assert_equal %w( foo.example com ), @klass.build("com").decompose("foo.example.com")
+    assert_equal %w[example com], @klass.build("com").decompose("example.com")
+    assert_equal %w[foo.example com], @klass.build("com").decompose("foo.example.com")
   end
 
 end
@@ -175,14 +175,14 @@ def test_length
   end
 
   def test_parts
-    assert_equal %w( uk ), @klass.build("!british-library.uk").parts
-    assert_equal %w( tokyo jp ), @klass.build("!metro.tokyo.jp").parts
+    assert_equal %w[uk], @klass.build("!british-library.uk").parts
+    assert_equal %w[tokyo jp], @klass.build("!metro.tokyo.jp").parts
   end
 
   def test_decompose
     assert_equal [nil, nil], @klass.build("!british-library.uk").decompose("uk")
-    assert_equal %w( british-library uk ), @klass.build("!british-library.uk").decompose("british-library.uk")
-    assert_equal %w( foo.british-library uk ), @klass.build("!british-library.uk").decompose("foo.british-library.uk")
+    assert_equal %w[british-library uk], @klass.build("!british-library.uk").decompose("british-library.uk")
+    assert_equal %w[foo.british-library uk], @klass.build("!british-library.uk").decompose("foo.british-library.uk")
   end
 
 end
@@ -209,14 +209,14 @@ def test_length
   end
 
   def test_parts
-    assert_equal %w( uk ), @klass.build("*.uk").parts
-    assert_equal %w( co uk ), @klass.build("*.co.uk").parts
+    assert_equal %w[uk], @klass.build("*.uk").parts
+    assert_equal %w[co uk], @klass.build("*.co.uk").parts
   end
 
   def test_decompose
     assert_equal [nil, nil], @klass.build("*.do").decompose("nic.do")
-    assert_equal %w( google co.uk ), @klass.build("*.uk").decompose("google.co.uk")
-    assert_equal %w( foo.google co.uk ), @klass.build("*.uk").decompose("foo.google.co.uk")
+    assert_equal %w[google co.uk], @klass.build("*.uk").decompose("google.co.uk")
+    assert_equal %w[foo.google co.uk], @klass.build("*.uk").decompose("foo.google.co.uk")
   end
 
 end