Bacterial biofilms are surface-associated, multicellular, morphologically complex microbial communities. Much work has focused on factors affecting surface adhesion of Pseudomonas aeruginosa, and it is known that this bacterium secretes the Psl exopolysaccharide, which promotes surface attachment by acting as ?molecular glue.?Through a combination of experimental and simulation work, we have elucidated the role of Psl in the self-organization of individual surface-attached bacteria into microcolonies,the first step in communal biofilm organization. We have developed new agent-based models that, combined with massively parallel tracking of bacteria, demonstrate that P. aeruginosa deposits a trail of Psl as it moves on a surface, which influences the surface motility of subsequent cells that encounter these trails and thus generates positive feedback. Both experiments and simulations indicate that the web of secreted Psl controls the distribution of surface visit frequencies, which can be approximated by a power law.Using engineered strains with inducible Psl production, we show that local Psl concentrations determine post-division cell fates and that high local Psl concentrations ultimately allow elite cells to serve as the founding population for initial micro-colony development.