This chapter critically examines the phenomenology, classification, and clinical relevance of delusions within psychiatric practice. It explores traditional subtypes—persecutory, grandiose, somatic, and erotomanic—while interrogating their neurocognitive and behavioral underpinnings. Drawing on interdisciplinary research, the chapter highlights the limitations of categorical models and advocates for dimensional approaches that incorporate affective, perceptual, and reasoning abnormalities. Special attention is given to the role of stressors, social learning, and environmental influences as modulators of delusional intensity and persistence. The chapter concludes by proposing an integrative framework for assessment and intervention, emphasizing individualized formulation and the use of behavioral principles to alter the dimensions of delusional behaviors. Implications for long-term recovery are discussed, with recommendations for future research and clinical guideline development.