Of the technologies available for measuring gene expression, microarrays using cDNA targets is one of the most common and well-developed high-throughput techniques. With this technique, the expression levels of thousands of genes are measured simultaneously. DNA probes are immobilized on solid surfaces, either membrane-based or chemically coated glass surfaces. On glass arrays, the probes are hybridized with fluorescent-labeled target samples. Fluorescence intensities, which reflect gene expression levels, are detected by imaging the array using a laser or white-light source and capturing the image using photomultiplier tube detection or a charge-coupled device camera. Different laser-based scanners are used in laboratories to scan microarray images. This chapter discusses the imaging process and the protocols being developed.