I'll review a bit about the ISM to show what is meant by a galactic "diffuse cloud" and show that sightlines passing through such clouds have rich microwave molecular absorption spectra whenever the reddening is greater than about EB-V ~ 0.1 mag or AV ~ 0.3 mag. I'll summarize the inventory of several dozen molecules known in diffuse clouds from spectra taken anywhere from the uv to the microwave domain and show some systematics of their chemistry. With regard to the DIBS, this talk is not about DIBS per se (really, not at all) but about how microwave spectra, especially very broadband ones, can be used to winnow the list of prospective DIB carriers, avoiding the current process of publishing rather silly attributions that are immediately repudiated by harsh letters to Science or ApJ. If there's enough time I'll discuss how the polyatomic chemistry of diffuse clouds, although poorly understood on its own terms, can be used in an empirical sense to explain how CO first appears in the ISM.