ProjectDependencies  

#summary Depending on another SBT Project

It is possible to declare a declare a dependency on another SBT project, similar to jar dependencies, by defining a val in your project configuration file. You must specify the path at which the project can be found. (Currently, the path is limited to a subdirectory of the current project directory, which limits the usefulness of this technique.)

val util = project("util")

A project dependency will be built when the depending project is built, and its classpath will be available; see SubProjects for more details.

Note that there are some other variants of the project() method which override the configuration of the referenced project when it is loaded (ie they ignore the contents of its project/build directory). See the Project API for details.