This study analyses the announcements of European mergers and joint ventures as forms of intra-European direct investment that affect the share prices of U.K. plcs. From a review of the theories of multinational enterprise and foreign direct investment in the context of European economic integration, the study emphasized the importance of the single market and its implications on foreign direct investment. A comparison is made between mergers and joint ventures as forms of foreign direct investment based on their theories and empirical evidences. The effects of the integration on European mergers and joint ventures are then examined by analysing the announcement effects. Using event study methodology, the study investigates the effects of announcements of UK plc acquisitions of European firms and their involvement in European joint ventures on the share prices of UK plcs. Both parametric and non-parametric techniques are used to measure the impact of these announcements in terms of abnormal returns and volatility of returns. The results show positive significant market reaction to the merger announcements on the announcement day for the abnormal return and on the day before the announcement for the volatility. However a significantly negative post announcement cumulative abnormal return is found. A shift of the market reaction after U. K. Is entry into the Exchange Rate Mechanism (ERM) is also found. The market reaction to the joint venture announcements is not significant on the day of announcement. However a significant positive cumulative abnormal return is found a few days prior to the announcement of the joint venture. A positive significant relationship between cumulative market reaction and U.K. Is entry into ERM is also established. Profile analysis of the significant announcements also shows the relevance of certain factors that could explain the market impact of joint ventures.