Superconducting quantum interference devices, or SQUIDs, are highly sensitiveto magnetic flux and can be used to perform magnetic imaging at cryogenic tem- peratures. In this dissertation, I describe the first scanning SQUID microscope in a cryogen-free dilution refrigerator. First, I briefly describe basic SQUID theory, how to perform scanning SQUID microscopy, and how to design SQUIDs suited for microscopy. Next, I discuss both the apparatus and method to systematically characterize SQUIDs. I demonstrate that while heuristics provide guidance for finding low noise operating points, one often misses the best noise performance of the SQUID found by a systematic search. I also briefly discuss how to use ma- chine learning to predict SQUID noise. I then describe in depth the design of the SQUID microscope, focusing on explaining the reasons behind various features of the coldfinger and microscope. Finally, I describe how to characterize vibrations in our microscope using images of a vortex in a superconductor.