<p>Magnetic Resonance Imaging (MRI) is a very powerful tool for cancer diagnosis today. At present, however, there is still a lot of confusion about how this technology was developed and who were the major discoverers in this field. Particularly, there was a strong dispute between the followers of two scientists, R. Damadian and P. Lauterbur. Also, it was not clear about the physical mechanism that allows NMR to be used to detect cancer. In this review, we carefully trace the major developments in using NMR for cancer detection starting from day one, that was almost 50&#xa0;years ago. One can see from the research records that the truth was beyond the claims of the popular science literatures. The development of NMR for cancer detection involved several research groups, who made important contributions at different stages. Particularly, the key discovery leading to the development of MRI was the finding that the relaxation times and spin diffusion coefficient of water protons changed when cells became tumor. The physical mechanisms responsible for these changes are discussed in this review.</p>