This article sets out a theoretical framework for the study of organisational change within political alliances. To achieve this objective it uses as a starting point a series of premises, the most notable of which include the definition of organisational change as a discrete, complex and focussed phenomenon of changes in power within the party. In accordance with these premises, it analyses the synthetic model of organisational change proposed by Panebianco (1988). After examining its limitations, a number of amendments are proposed to adapt it to the way political alliances operate. The above has resulted in the design of four new models. In order to test its validity and explanatory power in a preliminary manner, the second part looks at the organisational change of the UDC within the CiU alliance between 1978 and 2001. The discussion and conclusions reached demonstrate the problems of determinism of the Panebianco model and suggest, tentatively, the importance of the power balance within the alliance as a key factor.