Prof. S. Arunachalam is globally known for his expertise in Scientometrics and their use for assessing the research impact on a wide scale ranging from individuals and departments to institutions and countries.  His interests includes scientometrics, science policy, information science, public understanding of science, openness in scholarly communication, ICT for Development and rural knowledge centres and improving information access, both for scientists and for the rural poor. He is one of the earliest in the developing countries to use citation indexes to study developments in science and science policy. He was instrumental in CSIR, DBT and DST adopting Green open access as official policy.