The mechanisms of band broadening in linear, nonideal chromatography are examined. A development is presented of a rate theory for this process, wherein nonideality is caused by axial molecular diffusion; axial eddy diffusion; finiteness of transfer coefficient. The correspondence with the plate theory is given, so that the results can also be expressed in heights equivalent to a theoretical plate. The plate theory has been extended to the case of a finite volume of feed; the requirement for this feed volume to be negligible has been examined and a method is presented for evaluating concentration profiles obtained with a larger volume of feed. An analysis is given of experimental results, whereby the relative contributions to band broadening for various cooperating mechanisms could be ascertained.