Book excerpt: Theoretical and experimental work on solids with low-dimensi℗Ư onal cooperative phenomena has been rather explosively expanded in the last few years, and it seems to be quite fashionable to con℗Ư tribute to this field, especially to the problem of one-dimensional metals. On the whole, one could divide the huge amount of recent investigations into two parts although there is much overlap bet℗Ư ween these regimes, namely investigations on magnetic exchange interactions constrained to mainly one or two dimensions and, secondly, work done on Id metallic solids or linear chain compounds with Id delocalized electrons. There is, of course, overlap from one extreme case to the other with these solids and in some rare cases both phenomena are studied on one and the same crystal. In fact, however, most of the scientific groups in this area could be associated roughly with one of these categories and, in addition, a separation between theoreticians and experimentalists in each of these groups leads to a further splitting of interests although many theories about these solids have been tested by experimenta℗Ư lists. Nevertheless, more cooperation and understanding between scientists working on low-dimensional cooperative phenomena should appreciably stimulate further development. With a better inderdis℗Ư ciplinary understanding, new ideas could possibly help chemists in synthesizing tailor-cut solids. This would in return give experi℗Ư mentalists new phenomena to examine and finally would stimulate new theoretical work.