In this thesis, many issues relating to bidders' gams from United Kingdom (UK) domestic corporate acquisitions will be investigated. More specifically. the focus will be on various factors that might affect a bidder's acquisition performance. These will include the type of deal (tender offer versus merger. or diversification versus focus enhancement), the method of payment (cash versus stock versus mixed). the type of target (public, private. or subsidiary), and the bidder's, the target's or the market's valuation. An emphasis will also be placed on the relationship between the market valuation and the bidder' s outcome from acquisitions, where significant long-run negative relationships have been found. At the same time. frequent bidders and non-public target acquisitions will be examined, as they constitute a large proportion of the takeover deals in the UK market and an examination of their acquisition performance can shed light on many existing theories and hypotheses. This research was developed to investigate the fundamental reasons for the results obtained from bidding firms, and it was found that market valuation affects bidders' decisions and enhances the formation of merger momentums Furthermore, the results show that bidders are subject to various behavioural biases. and these biases are more obvious during high market valuation periods. OveralL the findings suggest that valuations at the firm and market level clearly affect the intensity of merger activity and the subsequent performance of mergers.