Depression has became the main focus of psychiatry care and research, due to its epidemiologic and economic wheight in health. As a matter of fact depression is now the second condition after cardio-vascular diseases contributing to the costs in haelth in our modern societies attending to the Daly"s measures.

From an old ethiologic prespective psychiatry shift to a pragmatic way to solve the main therotical issues in care and research. By this, we have now standard clinical methods to diagnose and classify depression, easy to use by any clinician (Psychiatrists and GPs), but we don"t know the essencial psychologic and biologic mechanisms of this disease as well as how the supposed ethiologic factors interact with these mechanisms.

Psychopharmacologic treatments opened some doors to this mechanisms, but the knowledge is still unsatisfactory in order to differenciate the several types of depression and to drive specific treatments to patients.

In this presentation included in the Symposium BACK TO THE BASICS: CHALLENGES IN CLASSIFICATION OF DEPRESSION it will be revised the actual knowledge concerning ethiology and phisiopathology of depression.