Proteins are the driving force for all cellular processes. They regulate several cellular events through binding to different partners in the cell. They are capable of binding to other proteins, peptides, DNA, and also RNA. These interactions are essential in the regulation of cell fates and could be important in drugs development. For example RNA interacting proteins regulate gene expression through the binding to different mRNAs. These mRNAs could be involved in important cellular processes such as cell survival or apoptosis. This book contains review articles dealing with protein interactions with the above mentioned factors. The enclosed articles could be informative and stimulating for readers interested in protein.