Here's a rationale for this from an author of very popular many single-header libraries: https://github.com/nothings/stb#why-single-file-headers https://github.

Here's a rationale for this from an author of very popular many single-header libraries: https://github.com/nothings/stb#why-single-file-headers https://github.com/nothings/stb#why-single-file-headers As to how to use from two separate translation units - you need to define PL_MPEG_IMPLEMENTATION to actually include implementation. So you do that in one of your .c files. Rest of includes will have only declarations included.