Cosmic masers have been employed as unique probes of various astronomical objects and environments, ranging from newly born stars and evolved stars, the interstellar medium to active galactic nuclei. The maser scientific community is diverse and multidisciplinary but has long been tied together through the common background of physics and observational techniques. Time-domain studies from daily to decade-long monitoring of maser sources are also in progress with various telescopes from many different research teams in the world. Multiwavelength studies on maser sources have also proliferated, involving strong synergies with large facilities such as ALMA, JVLA, Gaia, and various VLBI networks. This volume gives a comprehensive, up-to-date review of cosmic masers as presented at IAU Symposium 380, the sixth international maser symposium. It also describes intensive discussion about ongoing and future projects relevant to maser science, such as global and new regional VLBI networks, SKA, and ngVLA.