Therapeutic Drug Monitoring (TDM) is a tool to optimise antidepressant pharmacotherapy improving efficacy and avoiding side effects. The Arbeitsgemeinschaft fur Neuropsychopharmakologie und Pharmakopsychiatrie (AGNP)-TDM group has worked out consensus guidelines to make progress in the use of TDM which in spite of its obvious advantages, is far from optimal in everyday clinical practice. Research-based levels of recommendation were defined with regard to routine monitoring of plasma concentrations for dose titration. Main indications of TDM compromise control of compliance, lack of clinical response or adverse effects at recommended doses, drug interactions, pharmacovigilance programs, presence of a genetic predisposition particularity concerning the drug metabolism, children, adolescents and elderly patients. Therapeutic ranges of plasma concentrations that are considered to be optimal for treatment are proposed, implications on pharmacoeconomics aspects are discussed. The need to improve the implementation of TDM in routine patient care is emphasized.