Although we now have the sequence of the human genome at hand, we face the challenge of assigning function to the identified genes. Genes usually ascribe their function through proteins, and the role of proteins is to interact with other molecules. Therefore, if we could map the interactions of proteins we would be able to understand protein function. The challenge of mapping protein interactions is vast and many novel approaches have recently been developed for this task using molecular biology, mass spectrometry and chemiproteomic techniques.