This article reviews the state of knowledge and the algorithms for the diagnosis, classification, and treatment of nocturia. The state of the art in diagnosis, classification, and treatment of nocturia is presented. Nocturia has been poorly classified and poorly understood. Multiple factors may result in nocturia, among which are pathologic conditions such as cardiovascular disease, diabetes mellitus, lower urinary tract obstruction, anxiety or primary sleep disorders, and behavioral and environmental factors. Nocturia may be attributed to nocturnal polyuria (nocturnal urine overproduction), diminished nocturnal bladder capacity, or a combination of the two. Distinction between these conditions is made by a simple arithmetic analysis of the 24-hour voiding diary. Nocturia has been poorly studied and, only recently, has been classified according to its etiology and pathogenesis. Based on a review of the current state of knowledge, this article presents a scheme for the classification and treatment of patients suffering from loss of sleep resulting from nocturnal micturition.