Predictive biology, particularly for microorganisms, is the next great chapter in synthetic and systems biology.Tasks that once seemed infeasible are increasingly being realized, such as designing and implementing intricate synthetic gene circuits that perform complex sensing and actuation functions, and assembling multispecies bacterial communities with specific, predefined compositions. These achievements have been made possible by the integration of diverse expertise across biology, physics, and engineering, resulting in an emerging, quantitative understanding of biological design. As ever-expanding multi-omic datasets become available, their potential utility in transforming theory into practice remains firmly rooted in the underlying quantitative principles that govern biological systems. This review discusses key areas of predictive biology that are of growing interest to microbiology, challenges associated with the innate complexity of microorganisms, and the value of quantitative methods in making microbiology more predictable.