Medicines are fundamental components of treatment, management and control of various diseases. However, despite all their benefits, adverse reactions can be evoked by the use of medicines. Medicinal products achieve maximum advantage when they are appropriately used based on the sound understanding of their risks and benefits. To achieve this, evaluation and monitoring of the safety of medicines under real-life conditions, the appropriate pharmacovigilance systems, are essential. The World Health Organization (WHO) is a specialised agency of the United Nations which commits broad range of works to secure international public health. Pharmacovigilance is embraced as the WHO Programme for International Drug Monitoring (PIDM), which is led and organised by the Safety and Vigilance of Medicines group in the Department of Essential Medicines and Health Products in WHO. Pharmacovigilance is defined by the WHO as “the science and activities relating to the detection, assessment, understanding and prevention of adverse effects or any other drug-related problem” . Any other drug-related problems include such as substandard medicine, medication error, lack of efficacy, misuse, abuse, and Substandard/Spurious/Falsely-labelled/Falsified/Counterfeit (SSFFC) products. Whilst the world has made significant progresses in accessing essential medicines through the global efforts such as the UN Millennium Development Goals (MDGs), pharmacovigilance system is not well enough developed. The access to new medicines or the use of medicines in new environments can bring issues to concern. This article outlines the WHO PIDM, the core programme of pharmacovigilance in WHO, on its development, overview and current status. In addition, Safety and Vigilance of Medicines group's activities in order to tackle above concerns are also introduced.