Sperm are attracted by chemical factors that are released by the egg-a process called chemotaxis. Most of our knowledge on sperm chemotaxis originates from the study of marine invertebrates. In recent years, the main features of the chemotactic signaling pathway and the swimming behavior evoked by chemoattractants have been elucidated in sea urchins. In contrast, our understanding of mammalian sperm chemotaxis is still rudimentary and subject to an ongoing debate. In this review, we raise new questions and discuss current concepts of sperm chemotaxis. Finally, we highlight commonalities and differences of sensory signaling in sperm, photoreceptors, and olfactory neurons.