Quantum cascade lasers (QCL) emission wavelength spans from infrared to terahertz (THz), lead to many applications such as pollution monitoring, industrial process control, medical diagnostics, narcotic drugs and biochemical dangerous goods sensitive detection, and free space optical communications. Invented in 1994 following many years of research on band-structure engineered semiconductors and devices grown by molecular beam epitaxy, this fundamentally new laser has rapidly advanced to a leading position among infrared and terahertz semiconductor lasers in terms of practical wavelength agility as well as power and temperature performance. In this paper, we review the the progresses in designing concept of QCL, expanding wavelength range, increasing output power, realizing broadly tunable single-mode operation, and enhancing the beam quality in sequence. Finally, we give the brief conclusion and possible outlook.