The STAR*D (Sequenced Treatment Alternatives to Relieve Depression) study used a series of sequenced, randomized treatment trials following a first and, if needed, subsequent treatment steps to define the tolerability and effectiveness of various options in both acute and longer term treatment. Adult outpatients (n=4041) with nonpsychotic major depressive disorder, substantial chronic and recurrent depression, and co-morbid psychiatric and general medical conditions were enrolled in 41 representative primary and specialty care settings. About one-third of participants remitted in first step treatment with citalopram, 50% of these within 6 weeks. Poorer outcomes were associated with minority status, socioeconomic disadvantage, more axis I and III co-morbid disorders, lower function and quality of life, and anxious and melancholic features. In step 2 medication switch, there were no significant differences in remission among within-class, out-of-class or dual-action agents: sertraline (27%), bupropion-sustained release (26%) and venlafaxine-extended release (25%). In step 2 medication augmentation of citalopram, there was no significant difference in remission between bupropion-sustained release (39%) and buspirone (33%), although participants using bupropion-sustained release had greater symptom reduction and better tolerability. There were no significant differences in remission in step 2 between cognitive therapy and medication treatment in either the switch (31% vs 27%) or augmentation (31% vs 33%) strategies, although participants in cognitive therapy augmentation had a longer time to remission than those in medication augmentation (55 vs 40 days). In step 3, there were no differences in remission between a switch to mirtazapine (8%) or nortriptyline (12%), or between augmentation with lithium (13%) or T(3) (triiodothyronine, liothyronine) [25%], although more participants discontinued lithium due to adverse effects than discontinued T(3). In the fourth step, there was no difference in remission between tranylcypromine (14%) or venlafaxine-extended release plus mirtazapine (16%), although the combination treatment had fewer adverse effects and had the advantages of not requiring a washout period or diet restrictions. Participants requiring more than two well delivered treatments may be characterized as treatment resistant given the substantially lower remission rates after that point. Treatment resistance was associated with more concurrent axis I or III co-morbid conditions, socioeconomic disadvantage, chronicity and melancholic or anxious features. However, if participants remained in treatment for up to four steps, about 67% reached remission. Times to remission were not substantially longer for later treatment steps. The importance of reaching remission is highlighted by the lower relapse rates in naturalistic follow-up for participants entering in remission compared with those entering with response but not remission (step 1: 34% vs 59%; step 2: 47% vs 68%; step 3: 42% vs 76%; step 4: 50% vs 83%). Clinical decision making based on the itemized measurement of symptoms and adverse effects at each treatment visit was feasible in STAR*D's real world settings and resulted in adequate dosages and durations of treatment that generally exceeded those typically found in practice settings. Although switch and augmentation strategies could not be directly compared due to the equipoise stratified randomized design, the higher remission rates at step 2 with medication augmentation are intriguing and merit further study.