This thesis examines the role of the Ontario Secondary School Teachers' Federation in the process of educational decision-making in Ontario. The analysis focuses upon the involvement and influence of the organization in the introduction of a series of major, province-wide curriculum programs of the past three decades. Particular attention is paid to the rapid growth of the education system in these years and its effects upon the federation's relationship with the Ministry of Education. Finally, the conclusions are discussed in the context of existing theory concerned with inter-organisational relations in changing environments.