In contrast to mind-wandering, which is an automatic process, mindfulness means voluntarily paying attention to what is present (inside and outside oneself) and with a particular attitude, without judgment. Mindfulness-Based Stress Reduction (MBSR) was introduced into medicine in the late seventies and Mindfulness-Based Intervention (MBI) into psychiatry in the late nineties. The development of Mindfulness-Based Cognitive Therapy (MBCT) for the prevention of depressive relapse has been decisive from both a clinical and scientific point of view. Numerous randomized controlled trials (RCTs) have validated the efficacy of this intervention. MBCT halves the rate of depressive relapse compared with treatment as usual and is non-inferior to interventions such as continuing to take an antidepressant. In addition to efficacy studies, both quantitative and qualitative studies are favorable to MBCT. After MBCT for the prevention of depressive relapse, MBIs have been extended to other psychiatric disorders. Bipolar disorder and Attention-Deficit/Hyperactivity Disorder (ADHD) are good examples. For bipolar disorder, it was first necessary to verify feasibility, as this disorder was systematically excluded from MBCT studies, and then to set up efficacy studies. For ADHD, two approaches were developed in parallel: one developed a new MBI and the other adapted the MBCT protocol to ADHD. For both disorders, the first RCT studies are underway. Whether it's MBCT for the prevention of depressive relapses, MBCT for bipolar disorder, or MBI for ADHD, the question of the mechanisms of action is still open, and further studies are needed. To conclude, we can say that 20-30 years ago, people who took an interest in mindfulness were seen as a bit 'eccentric', but nowadays scientific evidence clearly shows that mindfulness has a place in the field of medicine.