“Density currents” and “density current baffles” are common terms in the lexicon of clarifier design. In terms of the baffles, the inclined Stamford Baffle is generally recognized as the most cost-effective improvement in clarifier performance available. Several years ago, NEFCO undertook a detailed, multi-year study of baffle performance that resulted in some significant changes in the way we think about the baffle and its design. These changes are reflected in this revision of “Baffle Basics.”