Animal behavior has long been a battleground between the competing claims of nature and nurture, with the possible role of cognition in behavior as a recent addition to this debate. There is an untapped trove of behavioral data that can tell us a great deal about how the animals draw from these neural strategies: The structures animals build provide a superb window on the workings of the animal mind. Animal Architects examines animal architecture across a range of species, from those whose blueprints are largely innate (such as spiders and their webs) to those whose challenging structures seem to require intellectual insight, planning, and even aesthetics (such as bowerbirds’ nests, or beavers’ dams). Beginning with instinct and the simple homes of solitary insects, James and Carol Gould move on to conditioning; the “cognitive map” and how it evolved; and the role of planning and insight. Finally, they reflect on what animal building tells us about the nature of human intelligence-showing why humans, unlike many animals, need to build castles in the air.