Mid-infrared quantum cascade laser technology has been developed rapidly since it was demonstrated in 1994. Since quantum cascade laser technology is small, robust and efficient, they have become commonly used mid-infrared laser source for various applications. The particular application fields of quantum cascade lasers are free space communication, chemical spectroscopy, environmental monitoring and infrared countermeasure. This work presents a comprehensive study over mid-infrared quantum cascade laser including review of theoretical background, theoretical analyses, active layer design, quantum mechanical, thermal and optical simulations, device fabrication, optimization and experimental characterization. As a result of this work mid-infrared quantum cascade laser have been successfully demonstrated.