Recent advances in genome technologies and computational biology have facilitated genome-wide views of hematologic malignancy. In particular, comparative gene expression methods using DNA microarrays have allowed for the analysis of gene expression patterns in both primary patient material and model systems of hematopoietic development. This review provides an overview of the basic technologies underlying these approaches and provides a summary of recent progress in the genome-wide molecular classification of human acute leukemias and lymphomas and of initial attempts to define oncogene-mediated transcriptional programs using DNA microarrays.