Protein-protein interactions are extremely valuable towards protein functions and cellular processes or we can say that protein-protein interactions play an important role in living cells. Therefore, if we can control the interactions between proteins, as a result, we can control some functionality of cells. Main functionality of a protein is carried out by its domains. So, domain is a structural or/and functional unit of protein. Behind protein-protein interactions there exist some domain-domain interactions. Therefore, under standing protein-protein interaction at domain level gives a global view of protein-protein interaction network.In this book, we have made an attempt to infer domain-domain interactions from interacting and non-interacting protein pairs then we have predicted protein-protein interactions based on inferred domain-domain interactions.