This thesis explores a proposed method for measuring the degree of Islamisation within a community, where Islamisation is defined as the extent to which Islam and religious concepts and rationale are used to organise and decide within the community at the political, social, cultural and personal levels. This proposed method involves the aggregation and analysis of measurements from different aspects by which a community could be Islamised, in order to obtain an assessment of the general state of Islamisation within that community. To assess the method’s feasibility, this thesis deploys it in two case studies of the Indonesian provinces of Central Java and West Sumatra during the Reformasi era. These case studies demonstrate that this method can be used to derive substantiated broad assessments about Islamisation. These assessments suggest West Sumatra is more Islamised than Central Java, although both provinces have experienced Islamisation during Reformasi.