Single fluorophores can be chemically attached to biomolecules, such as proteins or DNA, and the dynamics of individual molecules can be tracked by monitoring the fluorescent probe. Spatial movements within the Rayleigh limit can be tracked, along with changes in emission intensity and/or radiative lifetime, which often indicate changes in local environment. For instance, single-molecule labeling has yielded a vast quantity of information on how kinesin motor proteins move along microtubule strands in muscle cells. Single-molecule imaging in live cells reveals interesting information about protein dynamics under its physiological environment. Several biophysical parameters about protein dynamics can be quantified such as diffusion coefficient, mean squared displacements, residence time, the fraction of bound and unbound molecules, and target-search mechanism of protein binding to its target site in the live cell.