The presented dissertation thesis is aimed at the issue of the third sector organizations and their functioning. These organizations represent a significant and important part of the life of every company. Their effective functioning is conditioned by several factors. The thesis is therefore aimed at specification of the issues of functioning of the third sector organizations and subsequently at an analysis of interconnections between the legal form of the third sector organizations and assessment of the problems with their functioning, cooperation with business entities and selected aspects of the marketing activity. Analysis of the data gained from 357 third sector organizations accentuates the economic and financial problems of their functioning. Apart from these problems there is also the financial support of the business sector and self-financing. The aforementioned issues were assessed as the most significant both from the viewpoint of the own organization as well as of the third sector in general. On the basis of these findings, the possibilities and obstacles in cooperation of the third sector organizations with the business entities were analyzed. Acquired knowledge confirms the existence of several not insurmountable obstacles of this cooperation. The third sector organizations clearly lack the necessary information. Although the significant majority of these organizations addressed some business entities to propose cooperation, the biggest problem was seen by the third sector organizations in the financial and material help from these business entities. The most significant obstacles in cooperation with the business entities were, according to these organizations, inadequate understanding of functioning of the third sector organizations, prejudice and distrust. In this sense, an important role is played also by the lack of resources of the business entities. From the perspective of analysis of interconnections between the legal form of a third sector organization and the problems with marketing, it is crucial to point out that approximately half of these organizations, regardless their legal form, experience issues with the marketing activity and also approximately half of them have no website. The research results also confirmed a significant correlation between running an own website and problems with marketing.