This Primer provides relevant information in a simple and lucid manner, as a capsule and a ready reckoner. It will be useful for students, aspirants as well as anyone who has interest in understanding International Relations and Diplomacy. The topics range from International Organisations, Global Groupings to International Relations Theorists, Treaties, Pacts, Agreements, and much beyond. The Primer is equipped with maps, diagrams, pictures and quotations to generate interest in the reader. The broad expanse of the coverage will make understanding of International Relations terms and concepts easier for UPSC aspirants, not only for International Relations but will also be helpful in several other sections. In consonance with our times, there is special emphasis on the climate and the environment.