What is a quasispecies?- Historical origins and current scope.- The nucleation of semantic information in prebiotic matter.- Evolution of RNA-based networks.- Quasispecies on fitness landscapes.- Mathematical models of quasispecies theory and exact results for the dynamics.- Theoretical Models of Generalized Quasispecies.- Theories of lethal mutagenesis: from error catastrophe to lethal defection.- Estimating fitness of viral quasispecies from next-generation sequencing data.- Getting to know viral evolutionary strategies: Towards the next generation of quasispecies models.- Cooperative Interaction within RNA Virus Mutant Spectra.- Arenavirus Quasispecies And Their Biological Implications.- Models of viral population dynamics.- Fidelity variants and RNA quasispecies.- Antiviral strategies based on lethal mutagenesis and error threshold.