Sperm and oocytes must undergo several steps for successful fertilization, including sperm capacitation, the acrosome reaction and completion of oocyte maturation. During these steps, it is believed that specific molecules interact with precise timing. Although an increasing body of information on the fertilization-related molecules of sperm or oocytes has been accumulated through biological and gene targeting analyses, the information on these molecular interactions remains limited. Nonetheless, the current molecular information is the basis for future advances in the understanding of the mechanisms underlying fertilization. In this review, we introduce molecules that are involved in sperm-oocyte interactions at the site of fertilization, and address the molecular events during the sperm-cumulus, sperm-zona, and sperm-oolemmal interactions. Although the information introduced in this review has been obtained primarily from mice, similar molecules are likely engaged in analogous processes in other speicies.