There are likely more than 500000 potential phosphorylation sites in a cellular proteome. This dynamic phosphorylation is under tight control of a variety of kinases and phosphatases. In recent years significant progress has been made in the large-scale analysis of these in vitro and in vivo protein phosphorylation events. Much of this data have been deposited in public depositories, which have described so far about 25000 phosphorylation sites on about 7000 human proteins. However, the amount of phosphoproteomics data generated is now growing tremendously at a rate of about 10000 sites per reported study. The major advances made in global phosphoproteomics analyses originate from technological advances, whereby the largest contributions are from more selective phosphopeptide affinity enrichment technologies and from faster, and more sensitive mass spectrometers.