Masers are the microwave analogue of lasers; there are many astronomical sources of natural maser emission, including gas around forming and dying stars, and around supermassive black holes. These bright sources of microwaves are fascinating in their own right and provide unique abilities to probe details of astronomical sources. Molecular maser emission studies address important questions in the formation and evolution of stars, the structure of our Milky Way Galaxy, the characteristics of supermassive black holes, and fundamental parameters of cosmology. More than 100 astronomers from around the world gathered in Cagliari, Sardinia, for IAU Symposium 336 to discuss the latest findings related to masers. These proceedings summarize state of the art observations and theories pertaining to astrophysical masers and their environments, for graduate students and researchers. As new radio telescope facilities come online, observations of masers will continue to shed light on a broad range of important astrophysical problems.