Proteins could be derived from diverse food sources and have distinct compositions, such as water-soluble albumin, salt-soluble globulin, ethanol-soluble prolamin, and acid- or alkaline-soluble glutelin. The alkaline extraction and isoelectric precipitation method is commonly employed for extracting plant proteins. The pH used for protein solubilization can affect both the protein extraction efficiency and functional properties of the extracted proteins. This chapter outlines a protocol suitable for extracting several major types of plant proteins.