Despite the complexity imposed by the polygenic nature of plant tolerance to drought and to heat, significant strides have been made in understanding the underlying response and adaptation of plants to these stresses. Together with advanced and accessible technologies such as next-generation sequencing and precision phenotyping, this has enabled the assembly of molecular and physiological tools in grain legumes that would support the development of tolerance through traditional and molecular breeding. This chapter provides an overview of physiological, biochemical and molecular responses and adaptation mechanisms to drought, and to heat, with specific examples from grain legumes. The chapter examines the challenge of developing tolerance to drought and to heat, examining traditional breeding and the utilization of natural genetic diversity, and efforts towards molecular breeding including the identification of genetic associations and quantitative trait loci. Finally, the chapter considers functional genomics studies on stress-relevant candidate genes or gene families and suggests further reading on the topic.