What does an oPOSSUM have to do with transcription factor (TF) binding sites? Beats me, but it makes for a cute logo to decorate an otherwise plain website. oPOSSUM is succinctly self-described as “a web-based system for the detection of over-represented transcription factor binding sites in the promoters of sets of genes.” There are four components to the website: Single Site Analyses for human (and mouse), worm, and yeast genes, as well as a Combination Site Analysis for human/mouse genes. (The distinction between the two analyses is that either over-represented conserved single or combinations of transcription factor binding sites are included.) For each analysis, researchers enter a list of co-expressed genes, select specific transcription factor binding site matrices, and then choose the parameters for analysis. Do you find yourself interested in over-represented TF binding sites? Then stop playing dead and let oPOSSUM help you out!