MicroRNAs are short RNA molecules that do not encode for proteins but rather regulate the production of proteins from messenger RNAs. Importantly, microRNAs have been implicated in a broad range of stem cell roles in both healthy and diseased tissues. MicroRNAs show great promise as both biomarkers and therapeutics for disease. Here, we review how microRNAs regulate cell cycle, a critical property of how cells proliferate. Manipulating cell cycle to enhance stem/progenitor cell proliferation in degenerative diseases and suppress proliferation in cancer will be of great therapeutic value.