Widow spiders belong to the cosmopolitan genus Latrodectus (Araneae: Theridiidae), of which five species are found in North America. In part due to their medical importance and common occurrence, they are ever-more popular study organisms in a wide variety of fields. However, the literature is widely dispersed, and a broad synthesis has not been attempted since 1970. Here, we review and synthesize published information on the five North American Latrodectus species: L. hesperus, L. mactans, L. variolus, L. bishopi, and the introduced L. geometricus. We focus on distribution, ecology, anatomy, physiology, reproduction, ontogeny, behaviour, web structure, silk, venom, genetics, and phylogeny. We also include some of our own observations on L. hesperus. We conclude by highlighting areas where further research would be especially fruitful.