Sperm motility assessment by computer-aided sperm analysis (CASA) is an objective and quantitative method evaluating many sperm motility parameters such as percentage groupings and sperm kinematics rapidly. It is superior to manual assessment of sperm motility, which has been shown to be inconsistent and not repeatable. Modern CASA systems have been expanded to also incorporate automated modules dealing with, among others, sperm morphology, sperm vitality, DNA fragmentation, and the acrosome reaction. This chapter provides the background for the necessity and usefulness of CASA. The focus is mainly on human spermatozoa but information on animal spermatozoa is also provided.