This thesis closely explains the role of trade unions in preserving workers' rights. Trade unions as independent interest organizations of workers take a significant part in establishing the balance between employees and employers as two opposing sides of one working relation. Although this thesis mostly covers Croatian labor legislation, the usage of comparative method in analizing the origination of trade unions in certain European and American countries is also noticed. The same method is also used in the last chapter called Trade Union Organization and its Activity. The goal of the thesis itself is to explain the term 'Trade Union' and the ways of its action since the emergence of the first workers' associations, European and international documents in which they are acknowledged, through the conditions of union formation, trade union rights and the trade union internal structure. The end of this thesis is dealing with the influence a trade union has on social and political events and it also explores the future that awaits global trade unionism.