Informal settlements are a widespread phenomenon in African cities. This study explores the development patterns of informal settlements in Nairobi, Kenya, with a focus on the physical patterns, affordability of plots and rented rooms, and characteristics of developers. The results of the study were as follows: Spatial characteristics and conditions in informal settlements are not uniform. We identified squatter areas with iron-sheet houses and narrow streets, planned areas with high-rise buildings made of concrete blocks arranged in a perfect array, and intermediate conditions. Housing plot prices are unaffordable for most residents, while room rentals are generally fixed in accordance with the area and offer low-income residents a wide range of choices. The owners of some structures reside in their own structure, and others are non-residents who build and rent structures for profit. Therefore, informal settlements are not so much a place to live, but rather an attractive investment opportunity for structure owners or developers.