Single-molecule experiments have provided fresh perspectives to questions such as how proteins fold to specific conformations from highly heterogeneous structures, how signal transductions take place on the molecular level, and how proteins behave in membranes and live cells. This book focuses mainly on three experimental approaches: single-molecule fluorescence based mainly on fluorescence resonance energy transfer (FRET), atomic force microscopy (AFM) and diffracted X-ray tracking (DXT), and their applications to important biological phenomena. In addition, discussion is provided on the theoretical progress in the single-molecule data analyses. For students and professionals in chemical physics and physical chemistry from academia, government, and industries.