This is a copy of the slides presented at the meeting but not formally written up for the volume.

Since its market introduction roughly 30 years back, dynamic light scattering (DLS) has occupied a position of increasing popularity within the area of sub-micron particle and biopolymer characterization, due in large part to the non-invasiveness of the technique, the minimal sample volume & concentration requirements, and the quickness of data collection. Using ISO recommended measurement and analysis procedures, determination of the mean sample size and distribution width from DLS measurements is quite simple. In addition, modern instrumentation design and data interpretation software have removed much of the ?mystic? traditionally associated with this somewhat complex particle sizing technology. As a consequence, DLS instruments can now be routinely found in protein and nanoparticle laboratories around the globe. As might be expected, the simplicity of modern DLS instrumentation comes with a caveat. While calculation of the mean particle size for DLS is straight forward, extraction of further information, such as the intensity and/or volume (or mass) distribution is more convoluted, requiring the use of fitting algorithms. Data interpretation can be further complicated by the presence of noise, especially for samples with physical properties that are near the specified limits of the instrument/technique. This seminar covers the dos and don?ts of DLS data interpretation, and addresses the common question of ?what is the correct answer?.