Accurate aminoacyl-tRNA synthesis is essential for faithful translation of the genetic code and consequently has been intensively studied for over three decades. Until recently, the study of aminoacyl-tRNA synthesis in archaea had received little attention. However, as in so many areas of molecular biology, the advent of archaeal genome sequencing has now drawn researchers to this field. Investigations with archaea have already led to the discovery of novel pathways and enzymes for the synthesis of numerous aminoacyl-tRNAs. The most surprising of these findings has been a transamidation pathway for the synthesis of asparaginyl-tRNA and a novel lysyl-tRNA synthetase. In addition, seryl- and phenylalanyl-tRNA synthetases that are only marginally related to known examples outside the archaea have been characterized, and the mechanism of cysteinyl-tRNA formation in Methanococcus jannaschii and Methanobacterium thermoautotrophicum is still unknown. These results have revealed completely unexpected levels of complexity and diversity, questioning the notion that aminoacyl-tRNA synthesis is one of the most conserved functions in gene expression. It has now become clear that the distribution of the various mechanisms of aminoacyl-tRNA synthesis in extant organisms has been determined by numerous gene transfer events, indicating that, while the process of protein biosynthesis is orthologous, its constituents are not.