The study of mixed cultures, and in particular the dynamics of these systems with a focus on species coexistence under a variety of nutritional and flow conditions, was a hot topic in the 70s and another area where Ramkrishna devoted his investigative talent. As this topic of co-cultures has now also become fashionable in the context of synthetic biology, I would like to review some of the old research that was influenced by Ramkrishna’s work and then present some more recent developments from my lab. As always, one needs to identify the reasons that more than one species will do a better job than a single culture and be cognizant of the stability issues that are likely to arise when cultivating in the same growth medium multiple organisms. An example from a mixed culture of yeast and E. coli producing products of the isoprenoid pathway will be used to illustrate the various points.