Nikhil Ranjan Sen, also known as N.R. Sen, is known as the Father of Applied Mathematics in India. He did his Ph.D. on Theory of Relativity under the guidance of Max von Laue from the University of Berlin. Sen is considered as the founder of the Kolkata School of Relativity. He was a legendary mathematician and his research spanned other fields also like cosmology, ballistics and turbulence. He was not only contemporary to Meghnad Saha and Satyendranath Bose but was also a scientist of equal stature. His scientific research work was less known. The present book is an attempt to bring to light the life and works of this great scientist.