Mammalian sperm, the only cells that achieve their purpose outside their organism of origin, have to swim vigorously within the female reproductive tract to reach an oocyte. Flagellar dyneins drive sperm motility, which accounts for the consumption of high amounts of ATP. The two main ATP-producing metabolic pathways are compartmentalized in sperm: oxidative phosphorylation in the midpiece and glycolysis in the principal piece. The relative preponderance of these pathways has been discussed for decades (the so-called sperm energy debate). The debate has been muddled by species-specific variances and by technical constraints. But recent findings suggest that sperm from most mammalian species employ a versatile metabolic strategy to maintain motility according to the physiological environment. Different metabolic pathways likely coordinate by using exogenous and/or endogenous substrates in order to produce ATP efficiently. Defects in any of these pathways (glycolysis, mitochondrial oxidative phosphorylation, Krebs cycle, fatty acids oxidation, and ketone bodies oxidation, among others) may disturb sperm motility and be at the origin of male infertility. Understanding sperm bioenergetics is thus crucial for building new diagnostic tools, and for the development of treatments for patients presenting with low sperm motility. Some of these patients may benefit from personalized metabolic supplementations and dietary interventions. This article is categorized under: Reproductive System Diseases > Molecular and Cellular Physiology.