Little scientific research yet to be done on local projects conforming to Enterprise Architecture (EA). To lay foundations for such research, this article presents a theoretical framework for defining the Project Architecture (PA) in the context of working with EA. One part of the PA is the Project Start Architecture (PSA), which bounds the local project to the EA and/or Domain Architecture (DA). We start with explicating the context of a PSA in terms of its relation to the EA and DA. Subsequently, we define the PA in terms of three dimensions. The first dimension contains four aspect areas. The second dimension features four abstraction levels. The third dimension contains two project content categories: the PSA (containing prescription inherited from the EA an/or DA) and the PED (the Project Exclusive Design, containing the fundamental analysis and design artifacts that have been created specifically for the project). A real-life case is used to help illustrate and validate the theoretical framework. Additionally, a mapping with RUP artifacts is made to further clarify the framework of the PA with examples of well-known analysis and design artifact types.