336 Azides and alkynes have been selected from Enamine’s catalog of over 90 000 Building Blocks. Their structures have been published in the Selected Building Block series. This brochure, the sixth in series, provides a useful guide to novel and innovative chemistry developed at Enamine that can find multiple applications in drug design. Cycloaddition reaction of azides and alkynes has been shown to smoothly provide excellent yields of 1,2,3-triazoles. It has been recognized as an outstanding example of “click chemistry” This reaction can be used to selectively synthesize both 1,4- and 1,5-substituted triazoles. Besides reaction with azides alkynes undergo many other cycloaddition reactions.