AbstractTen years after the introduction of the first commercial ultra-high-performance liquid chromatography (UHPLC) system, the pace of progress has not slowed. We describe recent innovations in UHPLC columns and instruments, focusing on those intended primarily for reversed-phase separations of analytes with molecular weights less than about 5000 Daltons, using columns with internal diameters of 2.1 mm. New columns packed with sub-2-µm solid-core particles have produced efficiencies greater than 400,000 plates/m, more than 40% higher than those of columns packed with sub-2-µm fully porous particles. In addition, columns containing charged surface particles give higher peak capacities for separations of positively charged analytes when using the low ionic strength, acidic mobile phases preferred for electrospray mass spectrometric detection. The narrow peaks produced by these columns require instruments having extremely low dispersion. We review recent progress in measuring and reducing system dispersion.