A short review of empirical stellar spectral libraries

I present an overview of empirical stellar spectral libraries, their uses, and (briefly) their history. I focus primarily on their utility for understanding the stellar populations of composite stellar systems, but I show examples of their use for topics ranging from the determination of atmospheric parameters of stars outside the libraries to calibration of stellar atmosphere models to stellar radial velocities. I end by presenting the ``state of the art'' of available stellar spectral libraries focused on stellar population synthesis and what still needs to be done in the near future