This issue of Clinical Cancer Research contains a series of stimulating reviews that describe the benefits of using mouse models to study human cancer and the potential effect of these models for the treatment of patients with cancer. Each review is written by experts both in the generation of mouse models of cancer as well as the application of such models for translational research. All five reviews describe a new generation of genetically engineered mouse models that accurately recapitulate many features of human cancer and thereby provide valuable opportunities for drug discovery and other translational applications. In particular, Olive and Tuveson (1), focusing on mouse models of pancreatic cancer, discuss how such models can be used for drug discovery as well as the establishment of a ‘‘mouse hospital’’to facilitate preclinical testing in mouse models. Fomchenko and Holland (2), focusing on mouse models of brain tumors, provide examples of their application in preclinical studies. Similarly, Carver and Pandolfi (3), focusing on mouse models of leukemia and prostate cancer, describe preclinical studies using these models. Degenhardt and White (4) describe models that enable investigations of the programmed cell death mechanisms in cancer and the applications of such models to the development of rational chemotherapy. Finally, Singh and Johnson (5) review mouse models of several types of cancer, discussing the value of these models for drug development from the industry standpoint. Although each review has a different focus and offers a unique perspective, their overriding theme is that many highly sophisticated models that recapitulate many aspects of human cancers are now available, and therefore, translational studies using such models are likely to have a meaningful effect for the treatment of patients with cancer. However, the rapid expansion and widespread usage of mouse models of cancer has, not surprisingly, unearthed a certain amount of skepticism about their value and relevance for human cancer. Indeed, although we have witnessed a remarkable refinement of mouse models of cancer over the years, these models are still not ‘‘perfect’’and may never be so, considering the significant species differences between mice and humans (6). However, we need to remember that mouse models are just that—they are models, which offer unique opportunities to investigate cancer mechanisms in genetically defined and environmentally controlled scenarios in the context of the tumor microenvironment. Importantly, many studies that are easily done using mouse models of cancer would not be feasible in humans. Therefore, mouse models are intended to complement, not replace, studies done in humans and, if effectively ‘‘credentialled’’as discussed by Olive and Tuveson (1), can augment studies of human cancer. The reviews in this series are specifically focused on the application of mouse models of cancer for preclinical and translational studies; for more general discussions of mouse models of cancer, the reader is referred to previous reviews (7–10).