A fundamental component of quantitative cell biology is the ability to count molecules within cells. The numbers of molecules and stoichiometries are the basis for structural models of protein complexes and simulations of biological processes. A variety of methods exist for in vivo quantifications, but the focus of this volume is mainly on fluorescence methods. The two most popular methods are stepwise photobleaching and ratio comparison using a standard curve. With recent advances in genome editing techniques, most model organisms are amenable to inserting coding sequences for fluorescent...