Open innovation is the use of external partners to increase the innovation capacity of an organization. By cooperating with customers, universities, or other outside partners, companies can gain access to valuable knowledge and resources not available internally. This process is especially suited for smaller companies, which are often more focused on deep knowledge in a niche area, and may lack the wider knowledge of larger companies. This thesis looks at the prevalence of open innovation in startup micro-enterprises in Sweden, and how the use of these methods is linked to increased innovation performance. Based on a review of previous relevant research, a model was constructed around six hypotheses, each corresponding to an external collaboration partner. Empirical data was collected by the use of a quantitative survey, distributed to companies matching the target criteria. Empirical data was then analyzed using statistical software in order to validate if it supported the proposed model. The results show that only two of the six hypotheses, collaboration with customers and technology sourcing, were supported and significant. Two more variables, cooperation with competitors and universities, showed a positive correlation to increased innovation performance, but were not significant. These results are in line with several previous studies, which have also found a strong support for the link between innovation performance and both customer collaboration and technology sourcing, while showing weaker links to other forms of open innovation.