Madabusi Raghunathan has made fundamental contributions to the field of discrete subgroups of Lie groups, an area which has deep connections with geometry and number theory. He is a leading figure in this field, which has witnessed remarkable progress in the past few decades. His work on the cohomology, rigidity and arithmeticity of discrete groups, as well as his work on the congruence subgroup problem, are among his contributions which have advanced this field. His conjecture on the unipotent flows on homogenous spaces has had far-reaching consequences in number theory and was a catalyst to major progress in this area.