Orthodox library classification and cataloguing imply continuing and indefinite expansion of libraries and their buildings. This is no longer feasible. But ‘weeding’ of stocks is slow and labour‐costly. However, a simple subsidiary classification by year—‘Time‐Factor’—recorded on both book and catalogue entry will enable subsequent relegation of books to store to be made without any catalogue amendment. Relegation periods can be varied for different subjects. The method offers opportunities of devising regional, specialist and national storage policies for libraries.