Pharmacovigilance (derived from Pharmakon and Vigilare) or drug safety may be defined as a science related to the "collection, detection, assessment, monitoring, and prevention" of side/adverse drug effects. It is also essential to monitor for adverse effects even after a drug or therapy has been on the market for some time, as new ones may emerge. It is noteworthy to state, "An adverse reaction, in contrast to an adverse event, is characterised by the fact that a causal relationship between a medicinal product and an occurrence is suspected. Moreover, pharmacovigilance may go through three phases: pre-clinical, clinical trial, and post-marketing. Each phase has its implication in ensuring the safety of medicines. On the other hand, the process of pharmacovigilance may go through the following processes; stage 1: Detection. Collection of Individual Case Safety Reports (ICSRs), stage 2: Assessment, stage 3: Understanding the drug safety profile, stage 4: Prevention of adverse effects. This book intends to present good pharmacovigilance practices (GVPs) guidelines for pharmaceutical companies to follow to help prevent harm to humans caused by adverse drug reactions (i.e., ADRs) from approved pharmaceutical drugs. One approach to accomplish these guidelines is a Periodic Safety Update Report (PSUR) which may provide an update of the worldwide safety experience of a drug/medicinal product to regulatory authorities at defined time points post-authorization.