Virtual Issue: Type I and II Photosensitized Oxidation in Chemistry and Biology Edited by Ashwini Ghogare and Alexander Greer. This virtual issue consists of abstracts from 20 articles published in Photochemistry and Photobiology from January 2006-August 2012. The abstracts have been separated into two sections based on whether reactive oxygen species were photogenerated in chemistry or biology. Some of the articles asked critical questions to try to distinguish between Type I (electron transfer) and Type II (singlet oxygen) sensitized photooxygenation reactions. Radicals and radical ions were analyzed following classic methods ranging from ESR coupled with spintrapping techniques to superoxide dismutase and catalase experiments. Singlet oxygen generation was determined by its 1270-nm luminescence, by chemical trapping or deuterated solvents that increase its lifetime and toxic radius. Some of the papers examined how reactive oxygen species lead to biological outcomes, such as protein crosslinking or peroxidation which precedes degradation. But at other times, antioxidative effects were seen, reactive oxygen molecules that were quenched in doses to suppress skin damage. In contrast to homogeneous solutions, deducing relative Type I and II contributions in biological systems can be difficult due to the complex nature of biological matrices. But even in seemingly simple homogeneous solutions, the mechanism and story to tell can be condition-dependent, as solubility and sensitizer aggregation can increase Type I levels of superoxide and hydroxyl radicals. Acknowledgement: We thank Leda Lee for the artwork.