EMPERICAL STUDIES show a pattern of inter-industry wage differentials in which all workers in certain industries, irrespective of their personal characteristics, are paid higher wages than comparable workers in other industries (see Dickens and Katz, 1987:48-89 for a survey). These wage differentials have been found to persist over time (Cullen, 1956; Thaler, 1989:182). Furthermore, higher wages seem to be positively correlated with certain characteristics of industry, in particular concentration in product markets (Mellow, 1983;Kwoka, 1983;Long and Link, 1983). These empirical findings suggest that the structure of product markets could be an important factor contributing to inter-industry wage differentials. The empirical validity of the relationship between concentration in industry and wages is accepted by all schools of thought within the field of labour economics. Yet, theoretical attempts to explain these findings are numerous and diverse. The bone of contention seems to be whether the inter-industry wage differential reflects a skill differential and thus so-called rational economic behaviour by high wage industries, or whether higher wages are the result of power plays and strategic manipulation by firms with product market power (Weiss, 1966;Ryan, 1981) . An important related issue is whether the link between product market structure and labour market outcomes reflects a need for intervention in the product market. Labour economics is, however, not the only branch of economics with an interest in the effects of market structure on the behaviour and performance of firms or industries. Scholars in industrial economics have studied the link between competition or monopoly power and product market outcomes such as prices and profits. There is al-so much debate about the direction of causality between market structure, behaviour and performance. This paper argues that valuable insights 1995 SAJE v63 (1) p2 can be obtained from this debate in industrial economics by identifying, ordering, and systemizing the various lines of argument within the labour economics field about the link between product market structure and labour market outcomes. The paper demonstrates, firstly, that the debate on the link between concentration and wages is a debate about the direction of causality between industrial structure, industry or firm wage setting behaviour, and industry or firm performance. Secondly, the paper maintains that the line of argument reflected in opposing views within this debate shows strong resemblance to the opposing views in the debate in industrial economics about the causality between concentration, product market behaviour and performance. The debate in industrial economics on the causal relationship between market structure and product market performance accordingly provides a framework for a new and more coherent analysis of the debate in labour economics about the relationship between market structure and labour market out-comes. Lastly, the paper argues that the causal relation between concentra...