Analyzing periodicity in protein sequences is one of the numerous approaches to protein structure investigations, e.g., repeats that occur tandemly in sequence form integrated assemblies/folds, providing functional advantages to proteins, such as protein transport, protein-complex assembly, and protein regulation. Though in some cases these repeats may not exhibit any detectable identity between repeated copies, some amino acids that are functionally or structurally important are conserved during the evolution. These repeats play an important role in the efficient structural packing of two or more polypeptide chains of the same or different proteins, e.g., in leucine zippers, the leucines conserved at every seventh position zip together with a similar motif of another polypeptide. In this book the detection, distribution, functional analysis and disease association of three types of periodic peptide repeats, viz., tandem repeats, single amino acid repeats, and periodic occurrences of single amino acids is analyzed and organized in a database. Thus this book would prove useful for researchers interested in structural and functional investigations of proteins.