High gradient magnetic separation is a new technique which provides a practical means for separating weakly paramagnetic materials down to colloidal particle size on a large scale and at flow rates one hundred times faster than conventional filtration. It is based on the use of matrices of finely divided filamentary ferromagnetic material containing 95% void space, such as steel wool, subjected to strong magnetic fields generated bysophisticated magnets of a type not previously used for magnetic separation. HGMS was developed in the late sixties by MIT, Sala Magnetics and the Huber Company, and has been used since then for the purification of kaolin. The technique is of importance to the entire chemical and mineral industry, and in the treatment of water and sewage, but its application in other areas has been delayed by lack of interdisciplinary communication. What is needed at present is a better understanding of the mechanism of HGMS to permit a more scientific approach to future applications, and more inducement to the firms which are currently developing the next generation of hardware. Other approaches to magnetic separation also merit more serious attention, particularly those based on open gradient rather than matrix structures. New magnet technology developed in conjunction with HGMS and the advent of superconductivity make available field strengths, gradients and volumes at least an order of magnitude above those offered by the prior art. Such magnetic fields have potential value beyond their use in magnetic separation inasmuch as they are likely to affect the kinetics of many chemical reactions, very probably also those involved in the combustion process itself.