The US Food and Drug Administration-led Critical Path Initiative, launched in 2004, has resulted in an array of activities focused on the sciences that support the development of human medical products.(1) These activities include the development of new scientific tools, such as in vitro testing, qualified biomarkers of drug safety, and innovative new methods in study design and data analysis.(2) As a result of the Critical Path Initiative and enormous advances in the field of membrane transporters, the International Transporter Consortium was formed.