SUMMARY Imaging the tumor microenvironment (TME) is key to understanding tumor growth, disease progression and therapy options. The TME often consists of a complex neighborhood of diverse populations of immune cells, fibroblasts, and tumors cells. Little is known about the “geography” of the tumors and the spatial organization of the distinct cell types. The ability to rapidly identify different cell types and tumor subtypes using molecular markers will be transformative for cancer diagnostics. At Spatial Genomics, we are commercializing technology that allows transcript profiling in tumor samples. With this technology, cell types in situ and spatial organizations can be directly identified and visualized in tumor tissue slices. These capabilities provide a powerful tool for examining the different cell types and their interactions in the tumor microenvironment. In this proposal, we will develop the reagents, instrumentation, and the associated software that will allow researchers to perform spatial mapping experiments in tumor slices.