© Springer International Publishing Switzerland 2014. Postmarketing research is a generic term used to describe all activities after the drug approval by the regulatory agency, such as the Food and Drug Administration (MedWatch: voluntary reporting by health professionals. http://www.fda.gov/medwatch/report/hcp.htm. Accessed 12 Oct 2006), European Medicines Agency (EMA), or other regulatory agencies. Postmarketing studies concentrate much more (but not exclusively) on safety and effectiveness, and they can contribute to the drugs implementation through labeling changes, length of the administrative process, pricing negotiations, and marketing. However, the fact that not all FDA mandated (classical phase IV trials) research consists of randomized controlled trials (RCTs), and not all postmarketing activities are limited to safety issues (pharmacovigilance), these terms require clarification. This chapter attempts to clarify the confusing terminology; and, to discuss many of the postmarketing research designs-both their place in clinical research as well as their limitations.