Underdense regions in the universe contain a wealth of cosmological information. They emerge and evolve in a hierarchical fashion, and as mature voids form a dominant component of the large scale Cosmic Web. This seminaar will review our work on a rang of aspects of cosmic voids. First, we will discuss the hierarchical evolution of voids, discussing how they build up the void population via the processes of merging and collapse. Extending on the analytical framework, we subsequently discuss how the Multiscale Watershed Void Finder is used to construct void merging trees in cosmological computer simulations. A second aspect concerns the cosmological information contained in voids. The evolving shapes of voids form a sensitive probe of dark energy, and the seminar will explore the practical exploitation of this idea. Subsequently, the infrastructure of voids is investigated. The ongoing multi wavelength study of void galaxies in the Void Galaxy Survey will be presented. Void galaxies are unique probes of galaxy evolution, hardly affected by disturbing interaction with neighbours they are often small blue galaxies with a high rate of star formation. In addition to a discussion of some VGS resultss, we use the high-resolution LCDM simulation CosmoGrid to explore how dark matter halo systems similar in mass, size and environment to VGS31 came to be.