This thesis will explore trade unions and collective bargaining as a social, social process in which 2 parties participate. On one side are the employers, on the other are the employees organized into trade unions. A number of different circumstances take place in this process. There are circumstances when the collective agreement that is being negotiated is signed and both parties adhere to it, in some circumstances during the negotiation process the further course of negotiations is abandoned by one negotiating team, and sometimes a collective agreement is signed and it is negotiated indefinitely (and even until the very end of the duration) while part of the articles are not even applied and the like. There are also situations when a new union appears (founds) in a company during collective bargaining on a collective agreement. There are a number of questions here that clearly indicate all rights and obligations, for example, what are the rights of that union, can a new union expect to enter the bargaining committee and in what way, what must it know, in what ways can it access collective bargaining and can it at all access, if it did not exist at the time of signing the collective agreement? What is union representativeness and what importance does it have for collective bargaining? What does the Labor Law say? Is the Labor Law being changed and in whose favor? What is the opinion of the public? Is there discrimination against small unions and other things? On the trail of these complex issues, this paper attempts to give an overview of theoretical considerations and good practices, as well as a description of the establishment of a trade union in the Republic of Croatia, up to the achievement of representativeness in the negotiation process, after which a solution is made and the conditions for collective bargaining appear.