This chapter examines the fundamental ideas behind brain architecture and function, offering a thorough rundown that is crucial to comprehending neuropsychological phenomena. Readers have insight into how changes in brain morphology might emerge in behavioral and cognitive outcomes pertinent to forensic situations through a thorough examination of brain structures and neural networks. Additionally, the chapter describes the many approaches to assessment used in neuropsychological assessments, from conventional paper-and-pencil tests to sophisticated neuroimaging methods. The practical applicability of these approaches to assessing neurological abnormalities, measuring cognitive functioning, and determining decision-making competence in legal settings is demonstrated by case studies. A better understanding of the complicated relationship between brain structure and function is one of the most important things that was learned, along with how important it is to use a variety of methods in neuropsychological testing to get a full picture of people who are involved in legal proceedings.