From the 19th century into the 20th century, the terms used to diagnose generalized anxiety included "pantophobia" and "anxiety neurosis." Such terms designated paroxysmal manifestations (panic attacks) as well as interparoxysmal phenomenology (the apprehensive mental state). Also, generalized anxiety was considered one of numerous symptoms of neurasthenia, a vaguely defined illness. Generalized anxiety disorder (GAD) appeared as a diagnostic category in the third edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-III) in 1980, when anxiety neurosis was split into GAD and panic disorder. The distinct responses these two disorders had to imipramine therapy was one reason to distinguish between the two. Since the revised DSM-III (DSM-III-R), worry about a number of life circumstances has been gradually emphasized as the distinctive symptom of GAD. Thus, a cognitive aspect of anxiety has become the core criterion of GAD. The validity of GAD as an independent category has been questioned from DSM-III up to preparation of DSM-5. Areas of concern have included the difficulty to establish clear boundaries between GAD and (i) personality dimensions, (ii) other anxiety-spectrum disorders, and (iii) nonbipolar depression. The National Institute of Mental Health has recently proposed the Research Domain Criteria (RDoC), a framework destined to facilitate biological research into the etiology of mental symptoms. Within the RDoC framework, generalized anxiety might be studied as a dimension denominated "anxious apprehension" that would typically fit into the research domain called "negative valence systems" and the more specific construct termed "potential threat."