Adolescents are a nutritionally vulnerable population; eating disorders are more common among adolescents and young adults. Orthorexia nervosa (ON) is a non-formally recognized condition characterized by an obsessive preoccupation with eating healthy and “pure” foods; the quality and not the quantity of food is pivotal in ON. ON is a complex entity which can be associated with severe diet restrictions, a negative impact on social relationships, and with physical and mental health conditions, including obsessive–compulsive disorder. In light of this, a literature review regarding the background, diagnosis, features, risk factors, interplay with the social media, and management of ON is presented in this article, with a focus on adolescents and young adults.