Gene expression maps for model organisms, including Arabidopsis thaliana, have typically been created using gene-centric expression arrays. Here, we describe a comprehensive expression atlas, At-TAX, which is based on whole-genome tiling arrays. We demonstrate that tiling arrays are an accurate tool for gene expression analysis and identified more than a thousand unannotated transcribed regions. Visualizations of gene expression estimates, transcribed regions and tiling probe measurements are accessible online at the At-TAX homepage.