Genome sequencing has affected studies into the biology of all classes of organisms and this is certainly true for filamentous fungi. The level with which biological systems can be studied since the availability of genomes and post-genomic technologies is beyond what most people could have imagined previously. The fungal genera Aspergillus and Penicillium contain some species that are amongst the most widely used industrial microorganisms and others that are serious pathogens of plants, animals and humans. These genera are also at the forefront of fungal genomics with many genome sequences available and a whole genus genome sequencing project in progress for Aspergillus. This book highlights some of the changes in the studies into these fungi, since the availability of genome sequences. The contributions vary from insights in the taxonomy of these genera, use of genomics for forward genetics and genomic adaptations, to specific stories addressing virulence, carbon starvation, sulphur metabolism, feruloyl esterases, secondary metabolism and pH modulation, to the development of novel methodology for use in parallel to genome sequencing. It therefore provides a taste of the current status of research in Penicillium and Aspergillus and a promise of many more things to come.