Despite the remarkable revolution that has taken place in the treatment of human infertility, there have been no significant advances in the methods we use to control fertility since the introduction of the contraceptive pill in 1960. The focus of this talk is on the development of new contraceptive modalities that target the male germ line either by targeting the mature spermatozoon or the process of spermatogenesis. In the case of the spermatozoon, novel reagents have been engineered that are activated on contact with human semen and serve to both immobilize the spermatozoa and limit the infectivity of pathogenic microbes such as Chlamydia. Such activate-able reagents should form the basis of dual-purpose topical contraceptive modalities designed to provide simultaneous protection against both fertility and sexually transmitted disease. Reagents that target spermatogenesis, on the other hand, are suitable as non-surgical alternatives to sterilization in domestic animals. Such sterilization strategies involve the generation of reagents capable of targeting non-renewable cell types in the testes, specifically Sertoli cells and spermatogonial stem cells. The essence of this technology involves identifying peptides that can specifically target a particular cell type and then linking these reagents to chemical entities that will generate a highly localized cytotoxicity. Neither of these examples are yet ready for clinical application however they do constitute a general proof-of-principle that may ultimately lead to reagents that can be used for the effective regulation of fertility in both man and animals.