ear Colleagues,Depression is a disease which has always been problematic in medicine: Firstly, because mood disorders provoke, are comorbid with or related to, or follow, manysomatic illnesses, of which they may alter the presentation, worsen the symptoms, or maskcertain features. Secondly, because there is a large variation in types of depressive states; this variation isbrought about by the presence or absence of precipitating factors, the patient's environ-ment and family history, detected or undetected comorbidities, and resistance to treatment. Finally, depressive states are difficult to characterize: it is extremely hard to divide patientsinto homogeneous groups responding to the same treatment in the same manner.Thediagnosis is often influenced by the complex relationship between the pre-existing per-sonality and the depressive symptomatology, and the prognosis is often based as much onthe former as on the latter.We have decided, in this issue of Dialogues in Clinical Neuroscience, to have thesevarious themes addressed by some of the shining lights in our field, and thus to presentan updated view of the various approaches possible, based on current knowledge in thearea, not only on a diagnostic and clinical level, but also in terms of deciding whether phar-macological treatment is appropriate, and examining the role of comorbidities.We are now living in an exciting time; we have made much progress in our knowl-edge of the causes of depression, and new ideas have been emerging, particularly in thefields of neurogenesis and neuroplasticity, and notably the implications of protein factors.Many new therapeutic possibilities are now emerging, and we finally have some hopeof being able to use treatments which have no or very few side effects.This naturally opensup avenues for long-term treatment, or even, in some cases, preventive treatment whichcould eliminate recurrences, even in chronic conditions.We would like to thank all those who have made the publication of this issue possi-ble, especially Prof Manfred Ackenheil, the coordinating editor, and all the authors whohave been willing to privilege us with their scientific opinions on the subjects proposed.Yours sincerely,Jean-Paul Macher, MDMarc-Antoine Crocq, MDE d i t o r i a lD1 4 5