Our second featured article for the May issue of Cold Spring Harbor Protocols is Systematic Monitoring of Protein Complex Composition and Abundance by Blue-Native PAGE, written by Harvey Millar and colleagues from the University of Western Australia. The article describes multiple experimental approaches using polyacrylamide gel electrophoresis (PAGE). Blue-native PAGE (BN-PAGE) allows a range of protein complexes to be visualized. When combined with sodium dodecyl sulfate PAGE (SDS-PAGE), the procedure can resolve the complexes and their subunits by their molecular weight. In conjunction with differential in-gel electrophoresis (DIGE), BN-PAGE can be used to quantify changes in protein complex abundance or subunit composition between different samples. A detailed methodology is provided for BN-PAGE, SDS-PAGE, and DIGE, and like all of our featured articles, it is freely accessible to subscribers and non-subscribers alike.