TLC is used extensively in nucleic acid chemistry to monitor the progress of chemical reactions, to assay fractions collected from a larger chromatographic separation (e.g., column chromatography), and to determine optimal conditions prior to column chromatography. This unit describes methods for spotting test compounds onto a TLC plate, developing the plate in a suitable solvent system, visualizing the results, and calculating the retention factor (R(f)). Candidate compounds can be co-spotted for identification without relying on R(f) values.