The replication of the genome of positive-strand RNA viruses depends on their own RNA replicase complexes. Substantial advances in the experimental approaches used to determine the composition of the viral replicase complexes revealed that the replicase complexes of eukaryotic positive-strand RNA viruses are assembled in a host-membrane-derived microenvironment and that this process is regulated by orchestrated interactions between viral proteins, viral genomic RNAs, and co-opted host factors, including molecular chaperones, RNA-binding proteins, and proteins associated with membrane remodeling and lipid synthesis. This review focuses on recent progress in our understanding of how plant RNA viruses organize viral and host factors to form their replicase complexes.