Cell Biology is the most taught basic science course in medical school as it is one of the most rapidly developing subjects in science. Cell biology overlaps with molecular biology, histology, pathology, cancer biology, neuroscience, and many other major related disciplines. Having an up-to-date Cell Biology textbook that covers many functional aspects is essential for medical students to “cross the bridge” between basic sciences and clinical courses. This textbook was edited and modified from Medical Cell Biology, Steven R. Goodman ed., Elsevier, 2008. The first several chapters serve as comprehensive introductions into organelle structure, functions and gene expression. The second half of this book details many topics in medical science, including cell signaling pathways, cell cycle, programmed cell death, and cancer. New technologies such as atomic force microscopy, proteomics, and gene therapy are also covered.