It is now well accepted that most chronic diseases have a common feature which is “low-grade” inflammation. Whether inflammation is causal or rather consequent to these diseases is still a matter of debate. A key factor of inflammation is considered to be “oxidative stress”, which is the result of an alteration of redox homeostasis which is critical for the regulation of physiological cell and organ metabolism and proliferation. The term “oxidative stress” is how-ever often used in an inappropriate manner as the primary target of the initial oxidative radical, superoxide ion, is nitric oxide which, being in large excess, acts as a “buffer”, yielding reactive nitrogen species. It is only once the superoxide fluxes exceed the nitric oxide fluxes that true “oxidative stress” occurs. Nitro-oxidative stress is a more appropriate term which takes into account the evolving generation of reactive nitrogen and oxygen species and their effects on cell and organ pathophysiology. The molecular bases of redox homeostasis and nitro-oxidative stress will be presented and discussed using obesity-linked inflammation as a path-ophysiological example.