In order to isolate intracellular proteins, cells must be disrupted. Several disruption techniques, both mechanical and chemical, are available (Table 1.1). An efficient protocol for cell disruption must be developed to release the protein in a soluble form from its intracellular compartment. The disruption protocol should be as gentle as possible to the protein, as the extraction step is the starting point for all subsequent procedures. The success of cell disruption depends on a number of variables, such as the choice of buffers, the presence of protease inhibitors, and the osmolarity of the resuspension buffer. The condition and the constituent of the extraction buffer depend on the nature of the cell type, the target protein, and its intended application.