Common Mental Disorders (CMD) such as depression, anxiety, and somatoform disorders impose heavy burdens on individuals and on society in the form of sickness absence. CMD are frequently undetected in primary care which postpone the initiation of proper treatment. This seriously worsens return to work (RTW). Comorbidity with somatic disorders also worsens RTW. CMD are, controlled for lifestyle, independent causes for the development of chronic and disabling somatic disorders. Collaborative care seems to be most effective intervention with regard to RTW. In this dissertation, the intervention provided, in a randomized controlled design, a psychiatric examination giving feedback to the individuals, primary care, and rehabilitation officers with regard to treatment and rehabilitation. Half of individuals who just had passed eight weeks of continuous sickness absence had a mental disorder of which the half was unrecognized. RTW was improved for individuals with an unrecognized CMD and sick-listed from full-time work. A screening instrument was developed and the implications of screening are discussed. The book is of interest for primary care and RTW rehabilitation officers.