India has the largest area of rainfed dryland agriculture in the world, with a variety of distinct types of rainfed dryland farming systems producing most of its coarse cereals, food legumes, and minor millets, and large amounts of livestock. All these are vital for national and regional food and nutritional security. Yet, the rainfed drylands have been relatively neglected in mainstream agricultural and rural development policy. As a result, significant social-ecological challenges overlap in these landscapes: endemic poverty, malnutrition and land degradation. Sustainable intensification of dryland agriculture is essential for helping to address these challenges, particularly in the context of accelerating climate change. In this paper, we present 100 questions that point to the most important knowledge gaps and research priorities. If addressed, these would facilitate and inform sustainable intensification in Indian rainfed drylands, leading to improved agricultural production and enhanced ecosystem services. The horizon scanning method used to produce these questions brought together 40 experts and practitioners involved in a broad range of disciplines and sectors. This exercise resulted in a consolidated set of questions covering the agricultural drylands, organised into 13 key themes. Together, they represent a collective programme for cross- and multi-disciplinary research on sustainable intensification in the Indian rainfed drylands.