Technical Abstract: The International aphid genome consortium, IAGC, herein presents the 464 Mb draft genome assembly sequence of the pea aphid Acyrthosiphon pisum. This is the first published whole genome sequence from the diverse assemblage of hemimetabolous insects, providing an outgroup to the multiple published genomes of holometabolous insects (flies, beetle, bee, moth, etc.). Aphids are important agricultural pests that are also biological models for studies of insect-plant interactions, symbiosis, virus vectoring, and the evolution of complex life cycles and polyphenism. Pea aphids are host-plant specialists, they can reproduce both sexually and asexually, and they have coevolved with an obligate bacterial symbiont. Here we highlight findings from analysis of the annotated genome that may be related to these unusual biological features. We discovered extensive gene duplication across many kinds of gene families and loss of several otherwise well-conserved gene families. More than 2,000 gene families expanded in the aphid lineage, relative to other published genomes, including genes involved in chromatin modification, miRNA synthesis and sugar transport. Gene losses include genes central to the IMD immune pathway, selenoprotein utilization, the purine salvage pathway and the whole urea cycle. The pea aphid genome reveals that few if any genes have been transferred from the genome of the obligate symbiont, Buchnera aphidicola, to the aphid genome, although seven bacterial genes expressed in the aphid have been transferred from a different bacterial origin. Thus the reduced gene count of the Buchnera symbiont does not reflect largescale gene transfer to the host genome. The inventory of metabolic genes in the pea aphid genome suggests extensive metabolite exchange between the aphid and Buchnera, including amino acid biosynthetic pathways shared between them. Proteomic analysis utilizing the pea aphid genome sequence has facilitated the identification of aphid salivary proteins exploited for herbivory. Therefore, the pea aphid genome provides a foundation for post-genomic studies of biological problems of fundamental interest as well as of problems related to agriculture.