Abstract: Adaptations do not exist in a vacuum; an adaptive trait must fit well not only with an organism's environment but also with other aspects of the phenotype. To understand the evolution of complex multivariate phenotypes, we need to explore the patterns of covariation and interactions among traits, known as phenotypic integration. My work considers integration across several levels of biological organization from both proximate and ultimate perspectives. Integration is often considered to be an evolutionary constraint, but in this talk, I will show that integration can also be viewed as a product of natural selection.