The modification of living cells such as bacteria, yeast and eukaryotic cells have recently attracted a great deal of interest due to the possibility of modified cells in novel applications ranging from microelectronics to biosensing. Since a living cell is involved in modification, the proper characterization is an important step. Either an imaging technique to confirm encapsulation of cells, spectroscopic technique to understand the chemical environment of coating material or a combination of both types of techniques should be employed. The other techniques such as zeta potential measurement to obtain information about surface charge properties and quartz microbalance (QCM) to monitor mass change as micro-organisms are modified can also give information about alterations on micro-organism surface. In this chapter, techniques used in living-cell modifications are summarized by giving examples from the literature.