Microbes are currently being used to produce many valuable chemical compounds relevant to biotechnology, industry and medicine.  Most of these processes utilize a single microbe to produce the desired product.  However, the production (or degradation) of chemicals requiring the expression of many enzymes can lead to a large metabolic burden upon the organism, leading to suboptimal yields.  As desired chemical processes become increasingly complex, employing multispecies cultures will both decrease the strain on a given organism and add additional levels of control.  Naturally occurring microbial communities are composed of many species, each playing a specific role within the community.  We are building synthetic microbial ecosystems wherein different chemical reactions are allocated to each microorganism. Synthetic biology aims to construct organisms with designed functions using naturally occurring component parts. This work has largely focused on engineering genetic regulatory networks with specific behaviors. Recent efforts have been made to extend these engineered networks to multicellular behaviors, in essence engineering simple communities. As a first step towards engineering microbial communities that carry out novel processes, we are developing high-throughput methods for identifying conditions under which the constituents of a community will coexist, without the addition of expensive chemicals such as antibiotics. We are also working to engineer quorum sensing-based components and systems that provide the required level of communication and control required for the implementation of polymicrobial reactors for a variety of metabolic engineering applications.