Down Syndrome (DS) is the most common genetic developmental disorder in humans and is caused by partial or complete triplication of human chromosome 21 (Hsa21; Trisomy 21). It is a complex condition which results in multiple lifelong health problems, including varying degrees of intellectual disability and delays in speech, memory and learning. As both length and quality of life are improving for individuals with DS, attention is now being directed to understanding and potentially treating the associated cognitive difficulties and their underlying biological substrates. These have included imaging and post mortem studies which have identified decreased regional brain volumes and histological anomalies which accompany the early onset dementia. In addition, advances in genome-wide analysis and DS mouse models are providing valuable insight into potential targets for intervention that could improve neurogenesis and long term cognition. As little is known about early brain development in human DS, in this article we also review recent advances in MR imaging that allow non-invasive visualization of brain macro- and micro structure, even in-utero. It is hoped that together, these advances may enable DS to become one of the first genetic disorders to be targeted by antenatal treatments designed to “normalise” brain development.