This is the third version of the guideline of the World Federation of Societies of Biological Psychiatry (WFSBP) Task Force for the Pharmacological Treatment of Anxiety, Obsessive–Compulsive and Posttraumatic Stress Disorders (published in 2002, revised in 2008). A consensus panel of 33 international experts representing 22 countries developed recommendations based on efficacy and acceptability of available treatments. In total, 1007 RCTs for the treatment of these disorders in adults, adolescents, and children with medications, psychotherapy and other non-pharmacological interventions were evaluated, applying the same rigorous methods that are standard for the assessment of medications. This paper, Part I, contains recommendations for the treatment of panic disorder/agoraphobia (PDA), generalised anxiety disorder (GAD), social anxiety disorder (SAD), specific phobias, mixed anxiety disorders in children and adolescents, separation anxiety and selective mutism. Selective serotonin reuptake inhibitors (SSRI) and serotonin-norepinephrine reuptake inhibitors (SNRIs) are first-line medications. Cognitive behavioural therapy (CBT) is the first-line psychotherapy for anxiety disorders. The expert panel also made recommendations for patients not responding to standard treatments and recommendations against interventions with insufficient evidence. It is the goal of this initiative to provide treatment guidance for these disorders that has validity throughout the world.