Industrial relations vary greatly at different times and places. After a period of comparative tranquillity, unrest may develop and flare up into stoppages of work occasioned by strikes or, less usually, lock-outs. Stoppages can be analysed in terms of their principal cause; by far the most frequent are those described as wage disputes and, in particular, claims for increases in wages. However, since the increases in wage rates now regularly demanded are not realistic, in the sense that they could not be achieved in real terms even under conditions ideal from the point of view of those who demand them, it would appear that although, under present conditions, wage claims provide a socially acceptable basis for conflict, the true basis lies elsewhere. Many types of institution are involved in industrial conflict: trade unions, employers' organizations and a variety of boards, tribunals and courts.