Abstract During the last decade considerable effort has been expended in the study of critical phenomena. These investigations are especially rewarding because they provide important links between several diverse branches of physics. For example, antiferromagnets, pure fluids, binary solutions and alloys all exhibit analogous critical behaviour. It is now firmly established that the classical phenomenological theories that have been proposed to describe these systems fail in the critical region: mainly because they do not account for the fluctuation phenomena which occur close to critical points, and are a poor approximation for systems with shortrange forces. Considerable progress has been made in formulating more realistic models, for example the king and Heisenberg ferromegnets, and some success has been achieved in obtaining solutions for these models. Similar theories may be postulated to describe the critical behaviour of other systems. Recent progress in theoretical understanding and refinement of ...