Key Features: - The Indian Study of Healthy Ageing (ISHA) examines the burden, causes and consequences of chronic diseases in an Indian adult population of ∼220 000. Once completed, ISHA will be the largest blood-based prospective study in South Asia. Expansion to sites in Varanasi, Guwahati, Sangrur and Mullanpur will further strengthen the study. - Recruitment began in 2015 in Barshi, Maharashtra state, India. Enumeration, including basic baseline data collection, has been completed for all participants. Further detailed data collection, through questionnaires, physical measurements and blood sampling, is complete for ∼39 000 participants and ongoing. Active follow-up and linkage to health-related datasets (for death, cancer and hospitalization) provide data on fatal and non-fatal disease events. - At baseline among the ∼39 000 participants, 53% were women, and mean (standard deviation: SD) age was 46 (11). Tobacco smoking and alcohol drinking are relatively uncommon, but tobacco chewing is prevalent (67% of men and 14% of women ever chewed tobacco). The population is relatively lean, with a mean (SD) body mass index of 23.2 (4.1) kg/m2. Self-reported, previously diagnosed chronic diseases were uncommon (hypertension: 6%; diabetes: 3%; cardiovascular disease: 1%; cancer: <1%). Depressive symptoms were common (at least one reported by 58%). - Data-sharing regulations are in place; specific proposals for future collaboration are welcomed.