Key Biodiversity Areas (KBAs) are internationally known sites for biodiversity conservation, identified using standardized criteria formed by the International Union for Conservation of Nature (IUCN). This chapter introduces the definitions of KBAs, their relevance to sustainable development goals (SDGs), their global spatial distribution, selection criteria and thresholds, the rationale for selecting, and the importance of monitoring these areas. More than 16,000 KBA sites have been identified globally, comprising several terrestrial, freshwater, and marine ecosystems. The chapter looks at the global distribution of KBAs across 13 major geographical regions, with Europe leading at 4862 KBAs, followed by Asia with 3427 (as of July 2024). In India, more than 650 KBAs have been recognized, with the largest KBA being the Jawaharlal Nehru Bustard Sanctuary, located in Solapur and Ahmednagar districts, spanning an area of 10,660 km2. KBAs are selected based on species and ecosystem criteria, with specific thresholds ensuring only the most critical sites are prioritized. The rationale for concentrating on KBAs includes their vital role in biodiversity conservation, alignment with SDGs, vulnerability to threats like forest loss and fires, and potential for integrating advanced monitoring technologies. The chapter focuses on monitoring KBAs for effective conservation, early threat detection, policy-making, and public engagement. Conservation initiatives can increase their impact and contribute broadly to global biodiversity targets by concentrating efforts on these sites. The chapter highlights the need for persistent improvement of KBA identification approaches, monitoring techniques, and robust policy frameworks to support their conservation in the face of increasing ecological challenges.