We will directly investigate convergence in the evolution of multicellularity using experimental microbial populations. Multicellularity has arisen at least 25 times in the history of life, but understanding the evolution of complex multicellular individuals from unicellular ancestors has been extremely challenging, largely because the first steps in this process occurred in the deep past. Moreover, extant multicellular life is extraordinarily variable in form and complexity. Our team will build on our current success in yeast, bacteria and algae, comparing and contrasting de novo transitions to multicellularity evolved in the lab. We will generate a series of papers and educational tools on experimental investigations of convergence during a major evolutionary transition. Our studies will involve phenotypic, physiological and genetic assessments of evolutionary convergence. We expect to transform thinking on the evolution of complex biological systems, showing the importance of multiple factors on convergent evolution, with an emphasis on multilevel appreciation for the potential for convergence to arise. These new studies will provide a wealth of information on the evolutionary genetics of complexity, the importance of phylogenetic history, and the role of chance in evolution.