Identification and characterization of stem cells can be a challenging and often evolving process. Stem cells not only must display the appropriate markers, but a healthy and robust stem cell population must also lack specific markers as well. To add to the complexity of this area of stem cell biology marker profiles change based on the species, site of origin, and maturity (totipotent vs multipotent) of the desired population. In addition stem cell populations may be consist of several specific phenotypes which are often indicators of the population′s ′general health′. In this section lists hundreds of products, from antibodies to substrates that aid on the ability to characterize stem cells. The products listed in this section are our most commonly used. Other, more unique products may also be found throughout the Sigma-Aldrich website.