Advanced high-strength steels are key structural materials for the development of next-generation energy-efficient and environmentally friendly vehicles. Medium Mn steel, as one of the latest generation advanced high-strength steels, has attracted tremendous attentions over the past decade due to its excellent mechanical properties. Here, the state-of-the-art developments of medium Mn steel are systematically reviewed with focus on the following crucial aspects: (a) the alloy design strategies; (b) the thermomechanical processing routes for the optimizations of microstructure and mechanical properties; (c) the fracture mechanisms and toughening strategies; (d) the hydrogen embrittlement mechanisms and improvement strategies.