This thesis presents a single site case study that investigates the impact of an international unit on the organisational culture of a Catholic Girls College in the city of Christchurch, New Zealand. Four main data collection procedures were employed in this study to obtain relevant material useful for describing the school culture and for identifying any apparent changes to the organisational culture between 1996-2002. Statistical searches, document searches, on-site observations, and interviews occurred at various times throughout the school year. Incoming data was analysed to search for emergent themes consistent with the literature. Results from the study relate to identifying demographic patterns, describing the school culture, examining and describing the cultural change process and describing the corresponding impact on the culture elements of this school community. Two basic directions underpin this study. One is concerned with the intangible and tangible manifestations within the school culture that have been subject to change, and the other with the implications of change on the members of the school community. The examination of cultural elements was aligned with the framework of school culture provided by Beare, Caldwell & MilliKen (1989). A school culture model is provided to give insight into the main cultural characteristics of Villa Maria College. A second culture model, the Change Wave Process Model is introduced as an analysis framework for a selection of cultural change examples applicable to the development of the international unit at this school. This study has revealed that a school is a culturally unique learning organisation that is directly, indirectly or unconsciously changed by people for the purpose of providing positive impacts on the people and the organisation as a whole. The major outcomes from this study indicate that the development of a new international unit at Villa Maria College has produced a number of positive and negative interactive forces that have in various ways impacted on the organisational culture. The changes that have occurred since 1996 as the international unit has grown and became established have affected the composition of a number of cultural elements that lie at different levels within the school organisation. The surface manifestations that are obvious in physical features or human interaction patterns have been further enhanced as new staff roles and responsibilities, rituals, ceremonies and symbols have been introduced with the formation of the international unit. The subsurface manifestations such as the values and the underlying assumptions of the school have also been subjected to change though to a lesser degree. A broadening assumption base has appeared in the most recent decade as the school has introduced new policies and programmes in an attempt to meet the standards set down in the national policy and curriculum frameworks relating to the education of international students. As a result key values such as equality, social justice, appreciation, tolerance and respect have been openly expressed and accentuated with the introduction of this new group to the school. The study concludes with an action-based model that encourages members of the various cultural units of this organisation to be involved in ongoing critical cultural evaluation activities that enable members of the school to inspect cultural change processes in the future.