Entrainment of dry warm air from above the cloud into the cloud layer modulates cloud properties and lifetime. Despite its importance, observations of entrainment remain elusive. Presented here is a technique to derive entrainment velocities using cloud top heights, and horizontal winds from the Multi-angle Imaging Spectro-Radiometer (MISR). The results motivate application of the technique to generate global climatology, and perform process-level and model-evaluation studies.