For many years, electronic component leads made of Cu alloys were “pretinned” with a 3 to 10 micron layer of electro-deposited tin-lead (Sn-Pb) alloy to maintain proper solder wetting during subsequent assembly. The worldwide electronics industry is in the process of removing Pb from their components. When Pb is removed from the electroplated surface finishes, Sn whiskers grow spontaneously from the surface finish. The whiskers are single crystal filaments typically 1 µm in diameter and several mm long. Numerous electronic failures due to shorting from whiskers have been reported, especially in the high reliability realm of aerospace, military, and medical device applications. This lecture will describe progress being made towards developing a fundamental understanding of Sn whisker growth and providing industry with information needed for mitigation strategies. See http://nepp.nasa.gov/whisker/ for general information about the Sn whisker problem.