Pluripotent stem cells show a remarkable ability to self-organize and differentiate in vitro in three-dimensional aggregates, known as organoids or organ spheroids, and to recapitulate aspects of human brain development and function. Regionspecific 3D brain cultures can be derived from any individual and assembled to model complex cell-cell interactions and to generate circuits in human brain assembloids. Here I discuss how this approach can be used to understand unique features of the human brain and to gain insights into neuropsychiatric disorders. In addition, I consider the challenges faced by researchers in further improving and developing methods to probe and manipulate patient-derived 3D brain cultures.