The Simons Foundation invites applications for postdoctoral fellowships to support research on fundamental problems in marine microbial ecology. The foundation is particularly interested in applicants with training in different fields who want to apply their experience to understanding the role of microorganisms in shaping ocean processes, and vice versa, as well as applicants with experience in modeling or theory development. While these cross-disciplinary applicants will receive particular attention, applicants already involved in ocean research are also encouraged to apply. The foundation anticipates awarding five fellowships in 2018.