One of the major advancements that Xcode 4 brought with it was the concept of a workspace. You can think of workspaces as a project composed of projects, and one of the big benefits of this approach is that each project tracks its files and other settings separately. What this means is that Diane can add classes to her API project, and Tom can merrily design UI, without stepping on each other’s projects.

You can create a new workspace-based project by simply selecting File?New?Workspace, but assuming that you’ve already got a project underway, you can turn your existing project into a workspace-based project by doing File?Save as Workspace... Once you have saved your project as a workspace, you can open it by selecting the xcworkspace file using File?Open.