tmuxinator
diff --git a/lib/tmuxinator/project.rb b/lib/tmuxinator/project.rb
@@ -48,15 +48,61 @@ def load(path, options = {})
           @settings = parse_settings(args)
           @args = args
 
-          content = render_template(path, binding)
-          YAML.safe_load(content, aliases: true)
+          project_content = render_template(path, binding)
+          project_yaml = YAML.safe_load(project_content, aliases: true)
+
+          load_and_merge_partials(project_yaml)
         rescue SyntaxError, StandardError => e
           raise "Failed to parse config file: #{e.message}"
         end
 
         new(yaml, options)
       end
 
+      def load_partials(project_yaml)
+        partials = project_yaml.fetch("partials", []) || []
+        windows_ = []
+        partial_config_paths = partials.map do |p|
+          if FileTest.exist?(p)
+            p
+          else
+            Tmuxinator::Config.valid_project_config?(p) && Tmuxinator::Config.global_project(p)
+          end
+        end
+        partial_yamls = partial_config_paths.inject({}) do |memo, partial|
+          partial_content = render_template(partial, binding)
+          partial_yaml_ = YAML.safe_load(partial_content, aliases: true)
+          if partial_yaml_.key?("windows")
+            windows__ = partial_yaml_.delete("windows")
+            windows_ += windows__
+          end
+          memo.merge(partial_yaml_)
+        end
+        partial_yamls["windows"] = windows_
+        partial_yamls
+      end
+
+      def load_and_merge_partials(project_yaml)
+        partial_yamls = load_partials(project_yaml)
+        # partial_yamls should always be safe to merge against
+        # The merge block currently exists to ensure that windows arrays are
+        # composed instead of clobbered. This first version is naive and
+        # doesn't attempt to merge windows contents and accumulates them. The
+        # result is that you may wind up with multiple windows with the same
+        # name and, perhaps, the same content. This is better than clobbering
+        # windows as partials are processed but the ideal is probably to merge
+        # and dedupe like-windows. We'll see ...
+        partial_yamls.merge(project_yaml) do |key, partial_val, project_val|
+          if  key == "windows" &&
+              partial_val.is_a?(Array) &&
+              project_val.is_a?(Array)
+            partial_val + project_val
+          else
+            project_val
+          end
+        end
+      end
+
       def parse_settings(args)
         settings = args.select { |x| x.match(/.*=.*/) }
         args.reject! { |x| x.match(/.*=.*/) }

diff --git a/spec/factories/projects.rb b/spec/factories/projects.rb
@@ -108,6 +108,14 @@ def yaml_load(file)
     initialize_with { Tmuxinator::Project.new(file) }
   end
 
+  factory :project_with_partials, class: Tmuxinator::Project do
+    transient do
+      file { "spec/fixtures/sample_partials.yml" }
+    end
+
+    initialize_with { Tmuxinator::Project.load(file) }
+  end
+
   factory :project_with_alias, class: Tmuxinator::Project do
     transient do
       file { "spec/fixtures/sample_alias.yml" }

diff --git a/spec/fixtures/sample_partial.yml b/spec/fixtures/sample_partial.yml
@@ -0,0 +1,2 @@
+pre:
+  - echo "partial_is_working"
diff --git a/spec/fixtures/sample_partials.yml b/spec/fixtures/sample_partials.yml
@@ -0,0 +1,18 @@
+# ~/.tmuxinator/sample.yml
+# you can make as many tabs as you wish...
+
+partials:
+  - spec/fixtures/sample_partial.yml
+name: sample_partials
+root: ~/test
+windows:
+  - editor:
+      layout: main-vertical
+      panes:
+        - vim
+        - #empty, will just run plain bash
+        - top
+        - pane_with_multiple_commands:
+            - ssh server
+            - echo "Hello"
+  - guard:
diff --git a/spec/lib/tmuxinator/project_spec.rb b/spec/lib/tmuxinator/project_spec.rb
@@ -33,6 +33,10 @@
     FactoryBot.build(:nameless_window_project)
   end
 
+  let(:project_with_partials) do
+    FactoryBot.build(:project_with_partials)
+  end
+
   let(:project_with_alias) do
     FactoryBot.build(:project_with_alias)
   end
@@ -118,6 +122,14 @@
       end
     end
 
+    context "with partials" do
+      it "renders the tmux config" do
+        rendered = project_with_partials.render
+        expect(rendered).to_not be_empty
+        expect(rendered).to include("partial_is_working")
+      end
+    end
+
     context "with alias" do
       it "renders the tmux config" do
         rendered = project_with_alias.render