This book contains nearly 300 letters between Qian Sanqiang and various famous figures in the scientific and cultural communities, including Marie and Pierre Curie, Ralph Powell, Joseph Needham, Mei Yiqi, Guo Moruo, Hu Shi, Chia-Chiao Lin, Yang Chen-Ning, and Tsung-Dao Lee. Most of the letters are released for the first time, and many of them are of great historical value in exploring the development of science and technology in China. Between the lines, readers can have an insight into the older-general scientists’ love for the motherland and hard-working spirit.