Cell lines are established proliferating cells in culture derived from various organ and sources used in basic research and early stage drug development studies. The choice of appropriate cell line depends on the organism of study, the disease investigated, and the tissue or organ of interest. Human, rat, and mouse cells are similar in protein and disease expression, which makes them accepted options for all-purpose studies. HEK-293 (Human Embryonic Kidney) cells are ubiquitously utilized in preliminary protein expression studies because of their easy growth and transfection. Transfected cell lines are also available for the analysis of receptors, G proteins, and ion channels. Hamster, monkey, and insect cell lines are examples of sources of ovary, lung, and parasites for the investigation of protein expression or organ function. Most cell lines are shipped frozen with or without media and equipped for transfection, so it is imperative to choose compatible transfection and cell line products.