It is well accepted that microorganisms can exist as self-organized communities attached to surfaces and one another (i.e., biofilm), often surrounded by extracellular polymeric substances (EPS). Microbial biofilms survive and thrive in most environments that contain liquid-solid, liquid-gas, and/or solid-solid interfaces with a multitude of physicochemical conditions. In addition, the biofilms have unique physiology and ecology that contribute to increased survival and growth (e.g., resistance to antimicrobials, heavy metal exposure, desiccation, and substrate-utilization). The uniqueness of microbial biofilms can have both advantageous and deleterious effects on the system of interest and can significantly impact the cycling of C, N, S, and P. Despite decades of research, there is much to learn about the complexity of biofilm communities and their environmental and evolutionary success. In this presentation, the diversity of biofilms will be discussed with examples from different environments, as well as respective microbial composition and function.