Lidars are well suited for studying the cirrus clouds of the upper troposphere. Lidar techniques include depolarization, Raman, and scanning. Extended cirrus cloud datasets are available from ground-based sites, which can characterize the macrophysical, microphysical, structural, and radiative properties of these clouds. Other interesting applications include the study of the effects of aerosols and ambient humidity on cirrus content. This productive line of research will be reviewed.