As our knowledge of our own human genome has grown, so has our understanding of the breadth and depth of possible genetic variation that makes us both unique individuals and fundamentally human. On the spectrum of structural variation, from single nucleotide poly-morphisms (SNPs) to chromosomal rearrangements, the extremes are fairly well understood. Until recently, however, the submicroscopic structural changes that lie in the middle of the continuum were underappreciated, in part because they eluded easy detection. These mid-range changes include copy number variations (CNVs)—the gain or loss of segments of genomic DNA relative to a reference. In this booklet we present three news articles and two seminal research papers that demonstrate the growing importance of CNVs.