The phenolic compounds in leaf material of 52 taxa of the Caprifoliaceae representing 11 genera have been examined. The cyanogenetic glycoside sambunigrin was found to occur only in certain members of Sambucus. Chlorogenic acid isomers and simple phenolic acids were identified in all taxa examined; coumarins were of more limited distribution. The flavonols kaempferol and quercetin, considered to be primitive chemical types, occur most frequently in Viburnum, Sambucus, and Weigela. The flavones apigenin and luteolin, more advanced types, are predominant in Symphoricarpos, Triosteum, and Lonicera. Amentoflavone, a biflavonyl derivative, has been found in two species of Viburnum, substantiating an earlier report of its existence in this genus. This is also taken to represent a primitive chemical type which supports the contention that Viburnum is one of the more primitive genera in the family. A number of other relationships within the family are discussed in light of the chemical data.