-type I: microscopic pK a s, -type II: fractional microstate populations as a function of pH, and -type III: macroscopic pK a s where microstates refer to a single tautomer of a specific charge state of a molecule. For each type of submission participants were encouraged, but not required, to submit all predictions their model generated for every molecule. SAMPL6 organizers then evaluated predictions based on experimental results for all macroscopic and a select set of microscopic pK a s . Details for the challenge including experimental results, all submitted predictions, and an overview analysis are available online (github.com/MobleyLab/SAMPL6).