Multi-principal element alloys, characterized by high configurational entropy, lattice distortion, and synergistic multi-element effects, break through the conventional single-principal alloy design paradigm and exhibit outstanding strength, ductility, and corrosion resistance, making them a promising class of high-performance structural materials. This review systematically summarizes the classification, compositional design strategies, deformation behavior, and strengthening mechanisms of multi-principal element alloys, with particular emphasis on major approaches for enhancing room-temperature ductility, including metastable structure engineering, ordered oxygen complex strengthening, heterogeneous structure design, and spinodal decomposition. The progress in corrosion resistance studies is also reviewed, elucidating the complex coupling among alloying elements, phase constitution, and the stability of the passive film. This review not only consolidates the latest advances in strengthening and corrosion resistance enhancement of multi-principal element alloys but also identifies critical scientific challenges in processing, microstructural control, and service performance.