Mode interactions have recently become the focus of intense research in micro/nanoelectromechanical systems (M/NEMS) due to their ability to improve device performance and explore the frontiers of fundamental physics. Understanding and controlling coupling between vibrational modes are critical for the development of advanced M/NEMS devices. This review summarizes the recent advances in studies of coupling between multiple modes in M/NEMS resonators, focusing especially on experimental developments and practical applications. First, depending on spatial distribution of interacting modes, this review divides the coupled mechanism in three types: intermode, near‐neighbor, and long‐range coupling. Then, several fundamental physics approaches based on mechanical‐mode coupling, including linear and nonlinear coupling, modal localization, synchronization, and phonon manipulation are reviewed. This review also introduces sensing applications by using coupled mechanical modes. Finally, the state‐of‐the‐art open questions and challenges are reviewed.