Lidars can used to study regions of the atmosphere that are relatively inaccessible to other means. The mesosphere is a region below which most of the ionizing radiation from the sun has already been absorbed, clouds do not form, aircraft and balloons cannot attain, and there is insufficient ionization for study with radars. Sounding rockets can make spot measurements at considerable cost. Lidars can probe this region by light scattering from molecules (Rayleigh scattering) and atoms (resonance fluorescence scattering). They have revealed to us a fascinating and once unexpected level of dynamics. They have also exposed a new aspect in the intersection of outer space and earth, the remnants of meteors. This talk presents an overview of methods and a summary of results from research on the upper mesosphere and lower thermosphere conducted (mostly) at Arecibo.