The warm-hot intergalactic medium contains a major part of all baryons in the universe. Despite this, it is very hard to observe in X-rays due to its relatively low temperature and the poor spectral resolution of most instruments. The high sensitivity and good spectral resolution of XMM-Newton allowed for the first time to show the presence of the warm-hot intergalactic medium in the outskirts of several nearby clusters of galaxies. In this contribution these results are presented. The physical state of the gas such as temperature, density, mass and chemical composition are discussed.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html