It all happened with a click: In a search for histone deacetylase (HDAC) inhibitors using in situ clickchemistry, the first example of protein–Cu acceleration of the azide–alkyne cycloaddition reaction was uncovered. The copper center in the protein target HDAC8 catalyzed triazole formation between one azide–alkyne pair among 30 possibilities. These results provide a new route to HDAC inhibitors and