Micro- and mini-bioreactors are characterized by their miniature working volume and comprehensive monitoring of process data, e.g., biomass, pH, dissolved oxygen, and fluorescence that are on par with conventional bench-top systems. The technical advancements of micro- and mini-bioreactors are supported by single-use material and micro-manufacturing, non-invasive optical sensors, automation such as industrial robotics and the integration of design of experiment software with data acquisition and process control. Owing to the miniature scales, micro-bioreactors typically feature lower turbulence intensity and energy dissipation rate, resulting in different mass transfer, mixing and shear conditions as compared to industrial scale equipment. Mini-bioreactors, nevertheless, are closer to large vessels. Micro- and mini-bioreactors are used mostly in screening and process development nowadays, owing to their combined high throughput and richness of data. They are also the hardware that will enable “precision medicine” in the near future.