In this paper, the imaging characteristics of diffractive optical elements (DOEs) are discussed.The concept of wave!band integral averaged diffraction efficiency is presented, and some design and prototype examples of hybrid diffractive !refractive imaging optical systems by the author are given, including a hybrid long focal length lens with secondary spectrum corrected, a hybrid CMOS camera lens with only two elements, and a complex hybrid camera lens with medium focal length, low F number and large FOV. The examples given broke through the limitations on configurations, specifications, volume and weight for conventional optical systems. Additionally, the recent development in fabrication technique and applications of hybrid diffractive!refractive imaging lenses are introduced.