Reactive oxygen species (ROS) are involved in numerous physiological and pathophysiological responses. Increasing evidence implicates ROS as signaling molecules involved in the propagation of cellular pathways. The NADPH oxidase (Nox) family of enzymes is a major source of ROS in the cell and has been related to the progression of many diseases and even environmental toxicity. The complexity of this family's effects on cellular processes stems from the fact that there are seven members, each with unique tissue distribution, cellular localization, and expression. Nox proteins also differ in activation mechanisms and the major ROS detected as their product. To add to this complexity, mounting evidence suggests that other cellular oxidases or their products may be involved in Nox regulation. The overall redox and metabolic status of the cell, specifically the mitochondria, also has implications on ROS signaling. Signaling of such molecules as electrophilic fatty acids has an impact on many redox-sensitive pathologies and thus, as anti-inflammatory molecules, contributes to the complexity of ROS regulation. This review is based on the proceedings of a recent international Oxidase Signaling Symposium at the University of Pittsburgh's Vascular Medicine Institute and Department of Pharmacology and Chemical Biology and encompasses further interaction and discussion among the presenters.