Tremendous advances in technologies have allowed the attainment of powerful insights into the molecular and genetic determinants that drive human cancers. However, this acquired knowledge has been translated into effective therapeutics very slowly, in part due to difficulty in predicting which drug or drug combination is likely to be effective in the complex mutational background of human cancers. To address this difficulty we have proposed and initiated the “co-clinical trial” project, in which we exploit mouse models that faithfully replicate the variety of mutational events observed in human cancers, to conduct preclinical trials that parallel ongoing human phase I/II clinical trials. Here, we focus on concepts relevant to the application of this novel paradigm and the essential components required for its implementation to ultimately achieve the rational and rapid development of new therapeutic treatments. Cancer Discovery; 1(2); 108–16. ©2011 AACR.