The genomes of bacteriophage Phi6 and its relatives are packaged through a mechanism that involves the recognition and translocation of the three different plus strand transcripts of the segmented dsRNA genomes into preformed polyhedral structures called procapsids or inner cores. The packaging requires hydrolysis of NTPs and takes place in the order S:M:L. Minus strand synthesis begins after the completion of the plus strand packaging. The packaging and replication reactions can be studied in vitro with purified components. A model has been presented that proposes that the program of serially dependent packaging is determined by the conformational changes at the surface of the procapsid due to the amount of RNA packaged at each step. The in vitro packaging and replication system has facilitated the application of reverse genetics and the study of recombination in the family of Cystoviridae.