mixed in same project ( project.json ), no you cannot do that (i mean c# source and f# source in same project ).<p>You can have multiple project (same repo, different directories ) and reference one from another<p>you can have each project.json use a different compiler setting the compilerName property ( csc for c#, or fsc for f# ) .<p>A project can reference another project, so you can reference a F# project in a c# project, or the other way around.<p>like now in .net with msbuild or other tools