The main idea of this master thesis deals with the question, how do companies in the aviation industry react in regards to the legitimacy and corporate social responsibility (CSR) policies, and how does the CSR implementation from the neo-institutionalism (NSI) perspective come into play? CSR has become more and more popular over the past few years due to the increasing globalization and the awareness brought into society for CSR related issues. The beginning of this thesis will concentrate on the theoretical description of CSR. Various definitions, principles and the major international CSR standards are presented as well. A successful CSR concept considers the relevant environment in business activities and then must be embedded or absorbed into the company as a whole. Before presenting the selected airlines which shall bring into perspective the above concepts, an overview of the NSI topic will be given. Companies are faced with environmental and social requirements and the need to meet this responsibility, therefore they must straighten their actions to the norms of the environment and produce legitimacy which will benefit all aspects. The increasing air traffic has not only impacted society negatively but it has taken an ecological impact on our planet also and these issues have been brought to the attention of the media more and more throughout the years. Immoral actions cannot under any circumstance remain unobserved as these issues will and can undoubtedly cause image damages for the company. Within the scope of this thesis, the way that airlines should perceive and act on their social responsibilities will be elaborated on. Companies have the possibility to produce legitimacy and by the separation of actions, communication and decisions in these organizations should thoroughly show that there are differences, between what the airlines communicate within their terms and what the practical reality really is.