Cross-referencing between different files with LaTeX

Sometimes I want to refer labels I placed in external .tex files. I mean, I want o refer (using the command \ref) a \label from a .tex file I created in another project. A valid solution it to use the command \include. But I in this case I don’t want to include the .tex, I only want to be able to refer their labels. This can be done using the xr package.