Protein phosphorylation is a common signaling mechanism in both prokaryotic and eukaryotic organisms. Whilst serine, threonine and tyrosine phosphorylation dominate much of the literature there are several other amino acids that are phosphorylated in a variety of organisms. Two of these phosphoamino acids are phosphoarginine and phospholysine. This review will focus on the chemistry and biochemistry of both phosphoarginine and phospholysine. In particular we focus on the biological aspects of phosphoarginine as a means of storing and using metabolic energy (in place of phosphocreatine in invertebrates), the chemistry behind its synthesis and we examine the chemistry behind its highenergy phosphoramidate bond. In addition we will be reporting on the incidence of phosphoarginine in mammalian cells. Similarly we will be reviewing the current findings on the biology and the chemistry of phospholysine and its involvement in a variety of biological systems.