This book provides a comprehensive analysis of the effects of mergers and acquisitions (M&As) on the value of companies. It examines the motivations behind M&A transactions and analyzes how the announcements of such transactions impact the returns of both acquiring and target companies. The study is based on a variety of announcements ranging from the 1990s to the recent past and includes both domestic and cross-border target companies in the UK. By classifying companies by nationality and industry relationships, it offers a deeper understanding of the dynamics of M&A transactions. The results show that announcements of acquisitions generally have a significantly positive impact on the returns of target companies, while the effects on acquiring companies tend to be more negative, particularly after the announcement date.