In summary, norbornene probes were evaluated in the detection of cysteine sulfenic acid on proteins and in cells. The norbornene probes are straightforward to prepare and selectively react with the sulfenic acid oxidation state of cysteine. The norbornene probes were more selective than commonly used dimedone probe 6. These studies will help advance the understanding of cysteine oxidation and its role in oxidative stress and redox signaling. ASSOCIATED CONTENT Supporting Information. The Supporting Information is available free of charge on the ACS Publications website. This file includes full experimental details and characterization data (pages S1-S29).