diff --git a/.codeclimate.yml b/.codeclimate.yml
index b1b2114..1b449f2 100644
--- a/.codeclimate.yml
+++ b/.codeclimate.yml
@@ -4,3 +4,5 @@ engines:
 ratings:
   paths:
   - "**.rb"
+exclude_paths:
+  - spec/**/*
diff --git a/.rubocop.yml b/.rubocop.yml
new file mode 100644
index 0000000..6583489
--- /dev/null
+++ b/.rubocop.yml
@@ -0,0 +1,41 @@
+Style/StringLiterals:
+  Enabled: false
+
+Style/Documentation:
+  Enabled: false
+
+Metrics/LineLength:
+  Enabled: false
+
+Style/TrailingComma:
+  Enabled: false
+
+Style/FileName:
+  Exclude:
+    - 'bin/**/*'
+
+Style/ClassAndModuleChildren:
+  Exclude:
+    - 'spec/**/*'
+
+Metrics/ModuleLength:
+  Exclude:
+    - 'spec/**/*'
+
+Style/GuardClause:
+  Enabled: false
+
+Style/IfUnlessModifier:
+  Enabled: false
+
+Style/DotPosition:
+  Enabled: false
+
+Style/SignalException:
+  Enabled: false
+
+Metrics/AbcSize:
+  Enabled: false
+
+Rails/TimeZone:
+  Enabled: false
diff --git a/lib/cc/engine/csslint.rb b/lib/cc/engine/csslint.rb
index 0eecfc4..9517c96 100644
--- a/lib/cc/engine/csslint.rb
+++ b/lib/cc/engine/csslint.rb
@@ -48,14 +48,31 @@ def results
         @results ||= Nokogiri::XML(csslint_xml)
       end
 
+      def build_files_with_exclusions(exclusions)
+        files = Dir.glob("**/*.css")
+        files.reject { |f| exclusions.include?(f) }
+      end
+
+      def build_files_with_inclusions(inclusions)
+        inclusions.map do |include_path|
+          if include_path =~ %r{/$}
+            Dir.glob("#{include_path}/**/*.css")
+          else
+            include_path
+          end
+        end.flatten
+      end
+
       def csslint_xml
-        exclusions = @engine_config['exclude_paths'] || []
-        final_files = files.reject { |f| exclusions.include?(f) }
-        `csslint --format=checkstyle-xml #{final_files.join(" ")}`
+        `csslint --format=checkstyle-xml #{files_to_inspect.join(" ")}`
       end
 
-      def files
-        Dir.glob("**/*.css")
+      def files_to_inspect
+        if @engine_config["include_paths"]
+          build_files_with_inclusions(@engine_config["include_paths"])
+        else
+          build_files_with_exclusions(@engine_config["exclude_paths"] || [])
+        end
       end
     end
   end
diff --git a/spec/cc/engine/csslint_spec.rb b/spec/cc/engine/csslint_spec.rb
index 730b8e9..7daee33 100644
--- a/spec/cc/engine/csslint_spec.rb
+++ b/spec/cc/engine/csslint_spec.rb
@@ -5,24 +5,81 @@ module CC
   module Engine
     describe CSSlint do
       let(:code) { Dir.mktmpdir }
-      let(:lint) { CSSlint.new(directory: code, io: nil, engine_config: {}) }
-      let(:content) { '#id { color: red; }' }
+      let(:engine_config) { {} }
+      let(:lint) do
+        CSSlint.new(directory: code, io: nil, engine_config: engine_config)
+      end
+      let(:id_selector_content) { '#id { color: red; }' }
 
       describe '#run' do
         it 'analyzes *.css files' do
-          create_source_file('foo.css', content)
+          create_source_file('foo.css', id_selector_content)
           expect{ lint.run }.to output(/Don't use IDs in selectors./).to_stdout
         end
 
         it "doesn't analyze *.scss files" do
-          create_source_file('foo.scss', content)
+          create_source_file('foo.scss', id_selector_content)
           expect{ lint.run }.to_not output.to_stdout
         end
 
-        def create_source_file(path, content)
-          File.write(File.join(code, path), content)
+        describe "with exclude_paths" do
+          let(:engine_config) { {"exclude_paths" => %w(excluded.css)} }
+
+          before do
+            create_source_file("not_excluded.css", "p { margin: 5px }")
+            create_source_file("excluded.css", id_selector_content)
+          end
+
+          it "excludes all matching paths" do
+            expect{ lint.run }.not_to \
+              output(/Don't use IDs in selectors./).to_stdout
+          end
+        end
+
+        describe "with include_paths" do
+          let(:engine_config) {
+            {"include_paths" => %w(included.css included_dir/)}
+          }
+
+          before do
+            create_source_file("included.css", id_selector_content)
+            create_source_file(
+              "included_dir/file.css", "p { color: blue !important; }"
+            )
+            create_source_file(
+              "included_dir/sub/sub/subdir/file.css", "img { }"
+            )
+            create_source_file("not_included.css", "a { outline: none; }")
+          end
+
+          it "includes all mentioned files" do
+            expect{ lint.run }.to \
+              output(/Don't use IDs in selectors./).to_stdout
+          end
+
+          it "expands directories" do
+            expect{ lint.run }.to output(/Use of !important/).to_stdout
+            expect{ lint.run }.to output(/Rule is empty/).to_stdout
+          end
+
+          it "excludes any unmentioned files" do
+            expect{ lint.run }.not_to \
+              output(/Outlines should only be modified using :focus/).to_stdout
+          end
+
+          it "shouldn't call a top-level Dir.glob ever" do
+            expect(Dir).not_to receive(:glob).with("**/*.css")
+            expect{ lint.run }.to \
+              output(/Don't use IDs in selectors./).to_stdout
+          end
         end
       end
+
+      def create_source_file(path, content)
+        abs_path = File.join(code, path)
+        FileUtils.mkdir_p(File.dirname(abs_path))
+        File.write(abs_path, content)
+      end
     end
   end
 end