(Complete work in Spanish) The doctoral thesis contributes to some related Management Control areas such us Mergers and Acquisitions (M&A) and the informal components of Control Systems. The objective of the research was to analyse how this process of business concentration may impact on the Management Control System of the acquired firm. For this purpose an alternative theoretical model have been developed from the review of Management Control literature and M&A in Management Accounting. This model builds on contingency theoretical insights and extends it with elements of informal control. To test the prepositions a single ethnographic in-depth case study was carried out. It was conducted in a Spanish subsidiary of an English chemical group during 31 months. The main findings of this research are related to the role of (1) both non-formal and formal mechanisms and, specially, (2) top management within this process of organizational change. Besides, it should be highlighted that one of the more interesting studied issues in our case was the analysis of the Spanish versus Anglo-Saxon Management styles.