Mammalian spermatozoa acquire the ability to swim during their transit from the testis to the oviduct under the control of several external and intracellular factors. These factors play also a pivotal role in regulating acquisition of hyperactivated motility and during the process of chemotaxis. This review summarizes the involvement of such factors in acquisition and maintenance of sperm motility, hyperactivation and chemotaxis, focusing in particular on the molecular bases of asthenozoospermia, a pathology of seminal plasma characterized by reduced sperm motility, which is one of the main causes of male infertility. Current in vitro treatments of asthenozoospermia are shown, together with the most recent findings on pharmacological and physiological molecules capable of stimulating sperm motility. The structure, function and mechanism of sperm flagellum responsible for the development of active motility are also analyzed in details.