Fast SEC is a very interesting modification of conventional SEC. The need for it emerges from combinatorial chemistry and high-throughput experimentation, where high-speed analyses are required. The different approaches to change the speed of analysis are extensively described in this paper. Special attention is paid to the trade-off between analysis time and resolution and to the selection of optimal column lengths and flow rates. Simulations are used to design and to understand experiments. Integrity plots are constructed to judge the quality of various SEC systems. Fast separations in size-exclusion chromatography are found to be more favorable than suggested by conventional theory. The results are based on experimental data obtained for polystyrene using THF as mobile phase.