Although it is widely accepted that human beings have an ingrained 'need to belong,' there seem to be a substantial subset of young people who seclude themselves for most of the time at home and no longer engage in education or work, ultimately withdrawing from participation in society. In Japan, this phenomenon has been labeled as 'hikikomori,' but given its global presence it may be preferable to use the term 'extreme social withdrawal' (ESW). In this qualitative review, we provide a description and definition of ESW, provide figures on its prevalence, and discuss a number of associated concepts, including loneliness and "aloneliness," school absenteeism and dropout, the 'new' developmental stage of adultolescence, and the labor force categories of freeter ('freelance arbeiter') and NEET (a young person not in employment, education, or training). The core of the paper is focused on the origins of ESW in young people and provides a narrative overview of relevant etiological factors, such as aberrant brain processes, unfavorable temperament, psychiatric conditions, adverse family processes including detrimental parenting, negative peer experiences, societal pressures, and excessive internet and digital media use, which are all placed within a comprehensive developmental psychopathology framework. We will close with a discussion of possible interventions for young people with ESW and formulate a guideline that describes (the temporal order of) various components that need to be included in such a treatment.