Trade unions are institutional representatives of worker interests both within the labour market and in the wider society, and they accentuate the collective rather than the individual power-resources of employees. In much of Western Europe a predominant characteristic has been trade union pluralism promoted by ideological, philosophical and religious differences, although in recent years there has been rather less emphasis upon the importance of religious affinity. This chapter has examined from a comparative standpoint a number of important characteristics of trade unions, mainly in relation to industrialised, market-type economies. The importance of the formative stages of unionism in determining structural features and in giving direction to subsequent developments has also been emphasized. Moreover, workers need to be predisposed, or mobilised, to take advantage of the opportune environmental conditions for unionisation which arise.