With high measurement accuracy and processing efficiency, spaceborne lidar has unique advantages in many disciplines and has gradually become one of the main technical means of Earth observation. This chapter focuses on two types of spaceborne lidar, linear detection, and photon counting, analyzes their working principles and data processing methods, introduces the transmitting system and receiving system of the two types of lidar, then elaborates on the lidar data processing methods and in-orbit geometric calibration methods, and finally selects typical scenarios to describe the application of spaceborne lidar in Earth observation science, and looks forward to the development trend of laser altimeter technology in the future.