Guaiacum, sometimes spelled Guajacum, is a genus of flowering plants in the caltrop family Zygophyllaceae. It contains five species of slow-growing shrubs and trees, reaching a height of approximately 20 m (66 ft) but usually less than half of that. All are native to subtropical and tropical regions of the Americas and are commonly known as lignum-vitae, guayacán (Spanish), or gaïac (French). The genus name originated in Taíno, the language spoken by the native Taínos of the Bahamas; it was adopted into English in 1533, the first word in that language of American origin.

Zygophyllaceae is a family of flowering plants that contains the bean-caper and caltrop. The family includes around 285 species in 22 genera.