The high copy yeast plasmid 2 microm circle, like the well-studied low copy bacterial plasmids, utilizes two partitioning proteins and a cis-acting 'centromere'-like sequence for its stable propagation. Functionally, though, the protein and DNA constituents of the two partitioning systems are quite distinct. Key events in the yeast and bacterial segregation pathways are plasmid organization, localization, replication, 'counting' of replicated molecules and their distribution to daughter cells. We suggest that the two systems facilitate these common logistical steps by adapting to the physical, biochemical, and mechanical contexts in which the host chromosomes segregate.