Baboons are not included in the growing body of documentation on primate spatial defense. Instead, most field studies of baboons suggest that troops occupy overlapping undefended home ranges. In southwestern Africa we found defense of space by two troops living in a Namib Desert canyon and by a population of troops on the Okavango Swamp flood-plain in Botswana. Two desert troops encountered one another at contiguous ends of their linear home ranges and established a defended boundary near a waterhole. One troop also dominated a third, a smaller troop at the opposite end of its home range. In the swamp, large troops, living in a more energy and plant species-rich environment, occupied small home ranges relative to troops studied elsewhere in Africa. Here space was defended along well-defined boundaries. Size and configuration of troop space and the arrangement of resources within each space influence the likelihood of intertroop encounters and the expression of spatial defense.