Background: Mergers and acquisitions (M&A’s) are common ways for businesses to expand, compete, and maintain in competitive business environments. A strongly debated question in literature is whether or not these M&A’s provide measurable benefits, as factors such as industry, geographic location, and regulations play key roles in the impacts of the M&A’s. In this paper, we investigate the short-term effects of M&A’s based on stock returns of acquiring companies, with a focus on finance industries in the British Isles. Purpose: The purpose is to study whether or not there are significant short-term abnormal returns for acquiring companies when M&As of financial services target enterprises take place. Further, the study examines factors which can affect the impact of M&A’s, such as size of transaction, whether it is domestic or cross-border, whether or not the acquiring company is in a finance industry, and whether there is evidence of merger waves related to finance M&A’s in the British Isles. Method: An event study methodology is applied and focused on calculating the cumulative abnormal returns, as well as verifying whether those are statistically significant. The study analyses 100 M&A’s conducted on target companies from the UK and Ireland between the years 2000 and 2019. The event study is performed using the STATA statistical software, which is used to analyse the stock return performance in comparison to the domestic market index for each acquiring company. Conclusion: The study finds statistically insignificant results, concluding that M&A events do not generate significant abnormal returns for acquiring companies. This is in line with majority of previous research done, showing that M&A deals are not deemed significantly value creating nor value destroying. M&A’s within finance industry where the acquiring companies were domestic, in a finance industry, where the deals were smaller, were all shown to have less negative, albeit still insignificant results. This study also presents evidence for merger waves. Moreover, this thesis adds a clear geographic and industry component which is often missing in previous research, showing that within finance industry in the British Isles the impacts of M&A deals are unlikely to be statistically significant in causing abnormal returns.