The x-ray structure of the glutamine aminoacyl tRNA synthetase bound to its cognate tRNA(Gln) and ATP was reported by Steitz and co-workers in 1989, providing the first high resolution structure of a protein-RNA complex. Since then, high resolution structures have been reported for RNA complexes with five other tRNA synthetases, the elongation factor Tu, the bacteriophage MS2 coat protein, the human spliceosomal U1A and U2B"-U1A' proteins, and the HIV-1 nucleocapsid protein. Although the number of high resolution structures of protein-RNA complexes are rather small, some general themes have begun to emerge regarding the nature and mechanisms of protein-RNA recognition.