Microcrystal test techniques can distinguish different types of crystals formed in specific types of chemical reactions and can provide an initial identification for a majority of controlled substances. In microcrystal testing, an unknown substance is added to a chemical on a slide. Crystals form that are specific to the substance and can be matched to a known sample through comparison under a microscope. The compendium currently contains 19 drugs for which microcrystal tests using various reagents have been previously developed. The drugs in the compendium were chosen from the annual reports compiled by the National Forensic Laboratory Information System (NFLIS). Information about known microcrystal tests was obtained, and a survey of crime laboratories was conduced to determine which reagents and micro crystal tests are currently used. Detailed descriptions are provided for the microcrystals formed from each test, including photomicrographs, morphology illustrations, optical properties, notes, and infrared spectra of the microcrystals. The scientists who created the compendium have noted that although some crime labs lack automated drug testing instruments, most have light microscopes, which are sufficient to do microcrystal testing for illicit drugs. Online access to the compendium is provided on this web page.