Informal networks play a critical role in advancing careers by providing peer support. This is particularly important in fields where women are grossly underrepresented, because peer networks can reduce feelings of isolation and provide access to information and opportunities for professional development. The power of networks lies in their ability to mobilize people and information for educational and institutional change. Here we highlight the example of the Earth Science Women’s Network (ESWN), which grew from a group of six female graduate students and postdocs to a non-profit organization with more than 3,000 members worldwide in 15 years. ESWN’s activities support women at all career stages and include a program for undergraduate students. Today, ESWN is partnering with larger professional societies to improve work climate conditions and shape a more inclusive society, particularly in light of incidences of sexual harassment. We describe the evolution of ESWN in response to membership needs and as a model for online and in-person community building. The ESWN community supports peer mentoring that builds upon personal connections to catalyze cultural and institutional change for the advancement and promotion of women in the geosciences.