The Shape and Topology of the Universe

What is the shape of the Universe? Is it curved or flat, finite or infinite ? Is space “wrapped around” to create ghost images of faraway cosmic sources? We review how tessellations allow to build multiply-connected 3D Riemannian spaces useful for cosmology. We discuss more particularly the proposal of a finite, positively curved, dodecahedral space for explaining some puzzling features of the cosmic microwave background radiation, as revealed by the 2003-2006 WMAP data releases.