This chapter focuses on three areas: brain structure and function (neuroanatomy), brain activity (functional brain imaging), and gene effects (genetics). Information from each area is beginning to be integrated, with the goal of understanding biological disease processes. The chapter focuses on the neurons because it is their functioning that is largely the basis of theories of psychiatric disorders at the level of analysis, with the recognition that the glial cells that support the neurons may also be relevant. Researchers have used several methods to test the hypothesis that psychiatric disorders reflect dysfunctions in neuronal communication systems. Researchers have also examined postmortem brain tissue to see changes in the shapes of neurons and their connections. Sociological analyses of the social construction of psychiatric disorders are also important; particularly at this juncture when the number of disorders officially recognized in psychiatry is growing at an unprecedented rate.