Prostanoids are arachidonic acid metabolites and are generally accepted to play pivotal functions in amongst others inflammation, platelet aggregation, and vasoconstriction/relaxation. Inhibition of their production with, for instance, aspirin has been used for over a century to combat a large variety of pathophysiological processes, with great clinical success. Hence, the cellular changes induced by prostanoids have been subject to an intensive research effort and especially prostanoid-dependent signal transduction has been extensively studied. In this review, we discuss the impact of the five basic prostanoids, TxA₂, PGF_2α, PGE₂, PGI₂, and PGD₂, via their receptors on cellular physiology. These inflammatory lipids may stimulate serpentine plasma membrane-localized receptors, which in turn affect major signaling pathways, such as the MAP kinase pathway and the protein kinase A pathway, finally resulting in altered cellular physiology. In addition, prostanoids may activate the PPARγ members of the steroid/thyroid family of nuclear hormone receptors, which act as transcription factors and may thus directly influence gene transcription. Finally, evidence exists that prostanoids act as second messengers downstream of mitogen receptor activation, mediating events, such as cytoskeletal changes, maybe via direct interaction with GTPase activating proteins. The final cellular reaction to prostaglandin stimulation will most likely depend on combined effects of the above-mentioned levels of interaction between prostaglandins and their cellular receptors.