In order to create crisp, defined patterns of biologically-created materials, new technologies need to be developed and implemented. The Meyer lab is developing first-of-their-kind bacterial 3D printers that can deposit engineered bacteria in specific three-dimensional patterns using simple devices and chemistries. Our bacterial 3D printers have fully automated, coordinated control of the pumps and printhead, allowing for high spatial resolution (<mm-scale) printing of bacteria onto wet or dry surfaces. Our printers mix an alginate-containing bacterial culture with a calcium chloride solution upon printing, triggering cross-linking of the alginate molecules to form a stable, biocompatible scaffold to support the bacteria. After printing, the scaffold is removable by dissolving the cross-linked alginate matrix with sodium citrate. We are applying our printer to the fabrication of engineered biofilms, groups of bacteria that live within a spatially structured polymer matrix. We use our 3D printer to deposit engineered E. coli that are able to produce CsgA fibrils, the major protein component of biofilm polymer matrices. These engineered bacteria can stick to the printing surface even after the printing scaffold has been dissolved away, creating free-standing, patterned biofilms. These model biofilms will be crucial for future development of anti-biofilm strategies, for which no reproducible model biofilm test system is currently available, as well as for the reliable production of beneficial living materials, which could be applied for water and soil purification or mineral extraction.