Size exclusion chromatography (SEC) is now a common polymer analysis method employed in polymer reaction engineering studies. However, this once simple technique is no longer very simple. In this overview we selectively review the literature relevant to the practical use of SEC to obtain quantitative results. Fractionation, detection, calibration, resolution correction and system development are examined in turn. It becomes evident that, at this stage in SEC development, each of these areas is advancing very rapidly. This means that valuable additional quantitative information on polymer molecular properties is now obtainable. However, this additional information is accompanied by significant additional sources of error and uncertainty. The original SEC with only a differential refractive index detector is currently the most reliable and precise system, as well as being the most limited in what information it provides. New methods of linking results from such simple systems with multi-detector "research instruments" are needed. SEC analysis of complex polymers to help define fractionation requirements and to improve elucidation of their molecular properties, without requiring a second chromatograph, appear feasible. For the more advanced SEC systems, increased attention to setting up the system for accurate results is vital to quantitative accuracy. The idea of obtaining satisfactory results from each detector, independent of other detectors present, before relying on results calculated from combinations of detectors, deserves special attention.