Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form in a biologically functional way. Proteinprotein interactions are intrinsic to virtually every cellular process. Interactions between proteins have been studied through a number of high-throughput experiments and have also been predicted through an array of computational methods that leverage the vast amount of sequence of data generated in the last decade. Here we review the important experimental and computational methods for the prediction of interactions and functional linkages between proteins. An overview of some of the databases and tools that are useful for a study of protein-protein interactions have also been discussed.