In recent years, the interest in the quality of food is getting increasingly widespread in our society. From now on, consumers are paying more attention to food components and are trying to adopt a more environmentally friendly by consuming, for example, products from short circuits. However, this attention to the quality of food can be pathological. The neologism orthorexia nervosa, invented in 1997, describes this obsessive relationship with food. People with orthorexia develop obsessions related to food quality and may develop eating rituals in order to stay “healthy”. Orthorexia nervosa is not yet considered a psychiatric disorder due to a lack of consensus on its definition, but it is associated with impaired somatic, social, professional and/or academic functioning. Indeed, although orthorexia nervosa has been the subject of increasing scientific interest, it remains poorly understood because the main tools used to assess it offer a partial measure of the concept. For example, the “ORTHO” self-questionnaire, which is the most widely used in the scientific literature, assesses an interest in healthy eating rather than psychopathological obsessions. The current data and knowledge on orthorexia nervosa are therefore uncertain, making it difficult to understand this concept. In order to better understand the issues at stake in the assessment of orthorexia nervosa, a critical reading of these tools is proposed in this article. Moreover, a new conceptualization of orthorexia emerged a few years ago. It offers a better understanding of this concept with a healthy side (i.e., healthy orthorexia) and a pathological side (i.e., orthorexia nervosa). In an attempt to clarify the knowledge on orthorexia, the main objective of this critical review of the literature is to present orthorexia nervosa according to its initial conceptualization and its current understanding in accordance with scientific advances. The second objective is to distinguish orthorexia nervosa from anorexia nervosa. The third objective is to highlight the emergence of a growing, and sometimes pathological, interest in healthy eating within the context of societal development. To achieve these objectives, a review of the literature on orthorexia and healthy eating was conducted.