We report the whole-genome sequence of the common marmoset (Callithrix jacchus). The 2.26-Gb genome of a female marmosetwas assembled using Sanger read data (6×) and a whole-genome shotgun strategy. A first analysis has permitted comparisonwith the genomes of apes and Old World monkeys and the identification of specific features that might contribute to the uniquebiology of this diminutive primate, including genetic changes that may influence body size, frequent twinning and chimerism.We observed positive selection in growth hormone/insulin-like growth factor genes (growth pathways), respiratory complex Igenes (metabolic pathways), and genes encoding immunobiological factors and proteases (reproductive and immunity pathways).In addition, both protein-coding and microRNA genes related to reproduction exhibited evidence of rapid sequence evolution.This genome sequence for a New World monkey enables increased power for comparative analyses among available primategenomes and facilitates biomedical research application.