Protein biosynthesis, the translation of the genetic code into polypeptides, occurs on ribonucleoprotein particles called ribosomes. Although X-ray structures of bacterial ribosomes are available, high-resolution structures of eukaryotic 80S ribosomes are lacking. Using cryo-electron microscopy and single-particle reconstruction we have determined the structure of a translating plant (Triticum aestivum) 80S ribosome at 5.5 Å resolution. This map, together with a 6.1 Å map of a Saccharomyces cerevisiae 80S ribosome, has enabled us to model ~98 % of the rRNA and localize 74/80 (92.5 %) of the ribosomal proteins, encompassing 11 archaeal/eukaryote-specific small subunit proteins as well as the complete complement of the ribosomal proteins of the eukaryotic large subunit. Near-complete atomic models of the 80S ribosome provide insights into the structure, function and evolution of the eukaryotic translational apparatus.