Rh(III)-catalyzed, chelation-assisted C-H activation and selenylation of arenes has been achieved. Arenes bearing oxime, azo, pyridyl, and N-oxide chelating groups are viable substrates, and electrophilic selenyl chlorides and diselenides are used as selenylating reagents. The catalytic system is highly efficient under mild conditions over a broad range of substrates with excellent functional group tolerance.