TDM is a multi-disciplinary clinical specialty aimed at improving patient care by individually adjusting the dose of drugs for which clinical experience or clinical trials have shown it improved outcome in the general or special populations. It can be based on a a priori pharmacogenetic, demographic and clinical information, and/or on the a posteriori measurement of blood concentrations of drugs (pharmacokinetic monitoring) and/or biomarkers (pharmacodynamic monitoring). a priori TDM consists of determining the initial dose regimen to be given to a patient, based on clinical endpoint and on established population pharmacokinetic-pharmocodynamic (PK/PD) relationships. These relationships help to identify sub-populations of patients with different dosage requirements, by utilizing demographic data, clinical findings, clinical chemistry results, and/or, when appropriate, pharmacogenetic characteristics. a posteriori TDM: includes pre-analytical, analytical and post-analytical phases, each with the same importance; is most often based on the specific, accurate, precise and timely determinations of the active and/or toxic forms of drugs in biological samples collected at the appropriate times in the correct containers (PK monitoring), OR can employ the measurement of biomarkers as a surrogate or end-point markers of effect (PD monitoring) e.g. concentration of an endrogenous compound, enzymatic activity, gene expression, etc. either as a complement to PK monitoring or as the main TDM tool. requires interpretation of the results, taking into account pre-analytical conditions, clinical information and the clinical efficiency of the current dosage regimen; this can involve PK-PD modeling. can potentially benefit from population PK/PD approaches possibly combined with individual pharmacokinetic forecasting techniques, or pharmacogenetic data. Proposed by Standards of Laboratory Practice Committee, 2003 Approved by IATDMCT Executive Committee, 2004 Amended by IATDMCT Executive Committee, 2011