Abstract: The boundary-layer transition (BLT) has a great impact on the performance of hypersonic vehicles. Typical BLT problems are reviewed concerning hypersonic vehicles with four different types of trajectories known as ballistic reentry, maneuverable reentry, hypersonic glide, and hypersonic cruise. Relating issues are discussed including dynamic stability, trim, impact point dispersion, thermal protection, vehicle weight reduction, and propulsion system optimization, etc., all of which can be attributed to aerodynamic force, aeroheating, and mixing efficiency that BLT impacts directly. Potential methods are suggested to control BLT for system design including adjustments of trajectory, wing load, and aerodynamic configuration, and selection of proper materials, etc., for drag reduction, aeroheating alleviation, and mixing efficiency enhancement. It is beneficial for system-design institutes to utilize quiet wind-tunnel and flight tests to acquire more experience and knowledge about BLT. Efforts should be made to enhance the capability of developing efficient and precise theoretical analyses and prediction tools.