This chapter reviews the neuropsychological and imaging studies carried out by the authors’ group and co-workers on split-brain patients in the past 25 years, to investigate the role of the human corpus callosum (CC) in the interhemispheric transfer (IT) and integration of information. These studies will provide evidence of how the research on split-brain patients may supply a significant contribution to the understanding of lateralized and diffuse brain functions. By comparing results from total and partial callosotomized patients with those from control subjects, many findings have been obtained on the organization and functions of the human brain. The studies will be described in a brief overview of other groups’ research on similar patients.