The analysis of a large number of tumor tissues with conventional techniques of molecular pathology is tedious and slow. The authors recently developed the tissue microarray technology that makes it possible to sample up to 1,000 tumors on one glass slide, which then can be analyzed by fluorescence in situ hybridization, RNA in situ hybridization, or immunohistochemistry. The tissue microarray technology has the potential to significantly accelerate molecular studies that seek associations between molecular changes and clinicopathologic features of the cancer. Examples of potential applications for tissue microarrays include testing and optimization of probes and antibodies, the organization of large tissue repositories, and the facilitation of multicenter studies. Further, tissue microarrays can be used for educational purposes as well as to improve quality control and standardization of staining methods and interpretation. Tissue microarrays have become one of the most promising tools for the molecular and anatomic pathologist and will have many applications in cancer research, as well as in other fields of pathology. This review article gives an overview of current applications of tissue microarrays as well as possible future development of the technology.