ProjectReferences

ProjectReferences are declarations within a software project that point to other projects, signaling that the referenced projects must be built first and whose outputs are consumed by the referencing project. In Microsoft .NET and MSBuild-based projects, a project reference is expressed as a ProjectReference item in the project file (for example, Include="..\\Library\\Library.csproj"). When present, the build system ensures the referenced project's assembly is built and available to the referencing project, and the reference is considered part of the dependency graph.

Project references differ from package references; a PackageReference brings in a NuGet package, while a ProjectReference refers to another project in the solution. This enables true project-to-project dependencies and allows transitive references to propagate. Build order is determined by the reference graph: a change in a library will trigger a rebuild of dependents. The output of the referenced project is used by the depending project, typically through a compile-time reference.

Metadata on ProjectReference items can control behavior, such as ReferenceOutputAssembly (whether to reference the built assembly) and Private (whether to copy the referenced assembly to the output directory). Circular references are not allowed; broken paths or missing project files can cause failures. Relative paths are commonly used to keep the solution portable. In modern SDK-style projects, the ProjectReference syntax is standard and Visual Studio reflects and manages these references within Solution Explorer, helping to visualize and navigate the dependency graph. Overall, ProjectReferences streamline development and builds in multi-project solutions by ensuring correct compilation order, reducing manual wiring, and enabling incremental builds.