It has been over 50 years since a review has focused exclusively on the monoamine oxidase (MAO) inhibitor tranylcypromine (TCP). A new review has therefore been conducted for TCP in two parts which are written to be read preferably in close conjunction: part I – pharmacodynamics, pharmacokinetics, drug interactions, toxicology; and part II – clinical studies with meta-analysis of controlled studies in depression, practice of TCP treatment, place in therapy. The irreversible and nonselective MAO-A/B inhibitor TCP has been confirmed as an efficacious and safe antidepressant drug. For the first time, a meta-analysis of controlled clinical trials in depression demonstrated that TCP is superior to placebo (pooled logOR = 0.509, 95%CI = 0.026 to 0.993, 4 studies) and equal to other antidepressants (pooled logOR = 0.208, 95%CI = −0.128 to 0.544, 10 studies). In treatment resistant depression (TRD) after tricyclic antidepressants (TCAs) and selective serotonin reuptake inhibitors (SSRIs), TCP was superior to placebo (logOR = 2.826, 95%CI = 1.494 to 4.158, one study) and non-established antidepressants (pooled logOR = 1.976, 95%CI = 0.907 to 3.045, 4 studies), and was equal to other MAO inhibitors and an antidepressant combination (pooled logOR = −0.366, 95%CI = −0.869 to 0.137, 4 studies). Controlled studies revealed that TCP might provide a special advantage in the treatment of atypical depression, which was supported by a recent PET study of MAO-A activity in brain. However, TCP treatment remains beset with the need for a mandatory tyramine-restricted diet and is therefore limited to use as a third-line antidepressant according to recent treatment algorithms and guidelines for depression treatment. On the other hand, the effort needed to maintain a tyramine-restricted diet may have been overestimated in the perception of both doctors and patients, which may have led to relative underuse of TCP. Interaction with serotonergic drugs bears the risk of severe serotonin toxicity (SST) and combination with indirect sympathomimetic drugs may result in hypertensive crisis which both adds to the risks of TCP. At the same time, TCP has low to no risks of central anticholinergic, sedative, cardiac conduction, body weight, hemostatic effects, or pharmacokinetic drug interactions. Neuroprotection by MAO inhibitors due to reduced oxidative stress is becoming increasingly studied. Taken together, TCP is being increasingly recognized as an important option in systematic treatment approaches for patients suffering from severe courses of depression, such as TRD and atypical depression, by offering a MAO-related pathophysiological rationale.