Abstract: Most nearby stars are unlike our Sun: Three­-quarters of the stars in our galaxy are M dwarfs, with masses from a tenth to a half that of the Sun. However, there are outstanding challenges to understanding these common stars, from the origin of their magnetic dynamo to predicting their sizes and temperatures. Understanding the physics of M dwarfs is important in its own right, and also because these stars often host planetary systems of their own.  I will discuss how I use observations of stellar spin, stellar magnetic activity, and transiting exoplanets to progress our knowledge of fundamental stellar and planetary properties. I will highlight how upcoming surveys and existing facilities can be used to investigate the origin of stellar magnetic dynamos and the evolution of exoplanetary systems.