This thesis explores the relationship between organisational effectiveness and member participation in Irish credit unions. It is hypothesised that a positive relationship exists between both variables. Co-operative literature suggests that co-operatives require the involvement of the members in identifying and meeting their own needs in order to be effective organisations. Previous research studies into the issue across a variety of organisational types have shown mixed results. Related research into credit unions is sparse. The primary research undertaken is both quantitative and qualitative in approach. Organisational effectiveness is examined in both quantitative and qualitative terms. Member participation, being an organisational process, is examined in qualitative terms. Indicators of organisational effectiveness, specific to credit unions, are drawn up and form a framework through which effectiveness is examined. A typology and indicators of member participation are also developed and form a framework through which member participation is examined. The case study method is used primarily, to examine organisational effectiveness and member participation in Irish credit unions. A case study of a theoretical credit union, which is based on a composite of good practice in credit unions in Ireland and internationally, is also drawn up to develop the analysis further. The case studies allow an analysis of both organisational effectiveness and member participation, as well as an exploration of the relationship between the two. The findings support the hypothesis that there is a direct relationship between the two variables. In order to be effective, credit unions must involve their members in identifying their needs and in designing services to meet these needs. At present, they do not do this to any large extent. In order to continue to meet the needs of their members and to compete in the financial services sector, credit unions will need to find ways of involving members, drawing on good practice in other co-operatives. This will be critical to their continued success