Since the publication of Open Innovation: The new imperative for creating and profiting from technology from Henry Chesbrough, the interest for Open Innovation grew dramatically in the last 15 years. According to the author, Open Innovation can be defined as “the purposive inflows and outflows of knowledge to accelerate internal innovation, and expand the markets for external use of innovation” (Chesbrough, 2006, p. 1). Many other authors joined Chesbrough in his research on Open Innovation and as a result the amount of publications concerning this topic increased quickly. However, due to the fast growth of the research stream, there is hardly any structure, which helps to define and classify the different emerging theories and studies regarding Open Innovation. Therefore, the aim of this Masters thesis is to first of all give a comprehensive overview on the Open Innovation concept and how it distinguishes from the Closed Innovation concept. During the examination of the Open Innovation model and its related theories, it became evident, that most of the research papers focused on the relationship between the firm and Open Innovation and neglected the relation between the firm and the firms stakeholders located in the Open Innovation context. Consequently, the second part of this Masters thesis consists of a systematic literature review of the extra-organisational level of the Open Innovation concept. Vanhaverbeke and Cloodt (2006, p. 276) realized that in order to structure the various Open Innovation theories, a reference framework is needed. Their framework will be used for this Masters thesis. At the intra-organisational level of this reference framework, topics such as absorptive capacity and the “Not-invented-here” syndrome are discussed. Research papers from for instance Lichtenthaler and Ernst (2006), Katz and Allen (1982) made valuable contributions to these topics. The organizational level deals with Open Innovation business models, which are discussed for example by Chesbrough and Rosenbloom (2002), and theories how companies can shift from a Closed to an Open Innovation model. The latter mentioned topics are attended e.g. by Chiaroni et al. (2010) or Fetterhoff and Voelkel (2006). The inter-organisational level addresses topics such as in- and out-licencing, corporate venture capital, joint ventures or contractual R&D agreements in an inbound and outbound Open Innovation setting. Relevant literature for this subchapter is provided for example by Tidd et al. (2005), Culpan (2014) or Dushnitsky and Lenox (2005a). At the extra-organisational level of analysis, the focus is on the firms stakeholders such as customers and users. Research papers that elaborate on consumer-generated innovations stem from Laursen and Salter (2006) or Berthon et al. (2015). Regarding users, von Hippel (1998, 2005, 2010) is the founder of the user innovation concept. The focus of the industrial, regional and societal level is on topics such as the investigation of the influence of industry development and inter-industry differences on the adoption of Open Innovation strategies (see e.g. Poot et al., 2009), local, regional and national innovation systems, and the impact of Open Innovation on citizens and public policy (see e.g. Carayannis/Campbell, 2009; Cohen et al., 2016; Miller et al., 2016). With reference to the second part of this Masters thesis, the systematic literature review of the extra-organisational level yielded in total 123 research papers. Descriptive analysis reveals that the 123 articles were published in 45 different journals. The two journals with the most publications since 2003 are the Journal of Product and Innovation Management with 11 publications and the Creativity and Innovation Management Journal with 10 published research papers. Further analysis points towards a trend of author collaborations in scientific research as merely 12 per cent of the total papers was written by a single researcher. Moreover, Füller, von Hippel and Matzler are the three researchers with the most publications with regard to the extra-organisational OI topic since 2003. Franke can be considered the most quality-driven researcher. The thematic analysis of the research papers identified five main sub-topics regarding the extra-organisational level of Open Innovation. The User Innovation sub-topic contains 44 of the 123 research papers. According to research, a user innovator is a user, who innovates a design, service or product for an improved benefit/utilization afterwards (Baldwin/von Hippel, 2011, p. 1402). Several research streams that address the User Innovation sub-topic are discussed: (1) user innovator types/characteristics, (2) motivational factors, (3) user innovator identification and (4) integration, and (5) value for the company. The second sub-topic addresses Customer/Consumer Innovation. The terms user and customer innovator are practically used synonymously in research. Hence, the differentiation between the two innovator types is difficult. Furthermore, the discussion of the Customer/Consumer Innovation sub-topic followed the same research streams as the investigation of the User Innovation sub-topic. The third sub-topic is Crowdsourcing, which is the voluntary generation of innovative solutions for a firm problem, performed by heterogeneous individuals, who are motivated to participate in problem-solving activities (Franke et al., 2013, p. 1495; Majchrzak/Malhotra, 2013, p. 258). The attended research streams of this sub-topic are about the motivations of companies to choose crowdsourcing, the motivations of users and customers to participate in crowdsourcing activities, the ideation process and the potential value of crowdsourcing for firms. Online Communities depict the fourth sub-topic and are defined as a large group of individuals, sharing the same interests, rules, norms, values and culture, and who interact regularly and voluntary over the Internet in order to find new solutions for personal or product-related needs (Schröder/Hölzle, 2010, p. 260). Besides the definition of Online Communities, different types of participants and their motivations, challenges for firms, which want to use Online Communities for their innovation processes and recommendations for overcoming these challenges, as well as the impact of Online Communities on the innovation process are discussed. The fifth and last sub-topic addresses Innovation Contests. An innovation contest is an approach that encourages a public crowd to co-creatively develop innovative solutions to a firms problem (Füller et al., 2014, p. 274; Hutter et al., 2011, p. 3). The discussed research streams focus on Innovation Contest participator types, the right contest design, toolkits and the potential value of Innovation Contests on firm innovation. Concluding, the systematic literature review revealed several future research trends. Research papers from Bugshan (2015), Ernst and Brem (2017), He and Wang (2016), and Mount and Martinez (2014) underline the value of social media for a companys innovation process. Moreover, the importance of social media will increase with technological advances and new crowdsourcing methods. In the future, companies will be able to develop products adapted for the users needs with data recorded from sensors within e.g. a users clothes (Brown, 2017, p. 826). Consequently, questions regarding the ethical use of crowdsourcing methods will arise (Standing/Standing, 2018, p. 74). Companies and researchers will have to think about solutions how on the one side, companies can use these new technologies to satisfy customer needs more effectively, and how on the other side, customer privacy can be secured. Finally, the examination of the found research articles revealed that the large majority of researchers focused on the front end stage of the innovation process. However, it is clear that research on the commercialization stage is more difficult, as users and customers are not involved in a companys business relationships in general. Hence, it is probable that there simply is hardly anything that researchers could investigate on the commercialization stage of innovation and therefore, the proportion of research in this area will not increase in the near future.