Companies spend trillions of dollars on mergers and acquisitions (M&A) every year, and tens of thousands of new M&A deals are announced every year. However, despite the huge costs, only 10% to 30% of the M&As announced, get finalized (Christensen et al., 2011).There is extensive research conducted on why M&As fail, and their implications for the companies involved in the transaction. However, these large deals do not only impact the firms directly involved in the deal.  Microsoft, one of the world’s most influential companies, made on the 18th of January 2022 an acquisition announcement regarding its intent to acquire Activation Blizzard, one of the world’s largest game studios. The announcement made headlines all over the world and resulted in protests from competitors of the two companies. One of these competitors, Sony, experienced a 13% drop in stock price due to the acquisition announcement.  This thesis investigates the effect of acquisition announcements on the stock return of competitors to the target company. The study is examining the competitors stock return during the month leading up to the announcement, as well as the stock return during the month following the announcement. The authors have taken inspiration from a previous study “Acquisitions: A curse or blessing for direct competitors? The impact of target ownership structure” conducted by Mataigne et al. (2021).  By reviewing over 700 market reactions to acquisition announcements over a 10-year period, the authors were able to statistically test the differences in mean stock return. The authors were able to conclude that acquisition announcements have a negative impact on the stock return of competitors, and thereby answer the proposed research question: “What is the effect of acquisitions announcements on the stock returns of target company’s competitors in Sweden?”. Competitors to the target firm of an acquisition will experience the most significant change in their stock returns in the time period close to the announcement, after which the reaction will stabilize. The empirical findings of the study contribute to the field of knowledge using Behavioral Finance, the Efficient Market Hypothesis, the Capital Asset Pricing Model, the Stakeholder Theory, the Mitchell Model, and various market valuation methods.  Evidently, theories as part of the Behavioral Finance scope, such as the Efficient Market Hypothesis, provide support to the findings following the acquisition announcement. Theories such as the Stakeholder Theory and the Mitchell Model have helped identify competitors' stakeholder role to show how various events and organizations affect them as stakeholders in the market.  This study, which utilizes over 60.000 datapoints from daily price data for its analysis, takes a deductive approach within the positivist paradigm framework. The data is statistically tested using paired t-tests.