The British Assemblies of God is a Christian denomination within the wider Pentecostal Movement which had commenced at the beginning of the 20th Century. This thesis traces the origins of the Assemblies of God during its formative years 1920-1925. By means of a sense of exploratory conferences attempts were made to create organisational unity between the Independent Pentecostal assemblies. Initial conferences at Swanwick and Sheffield failed. However a renewed attempt In 1924 led by John Nelson Parr, first at Birmingham and then at London, was successful. The first part of this thesis traces the detail of those discussions and the kind of organisation which emerged. The second part critically examines the reasons behind the formation of the new group. There were three main reasons. First there was the determination to preserve a distinctive Pentecostal testimony, especially relating to glossolalia. Secondly there was a growing need for co-ordination of fellowship and witness as the Independent assemblies expanded or faced challenges from other groups. Lastly there was the need for protection amongst the assemblies from false teaching and fanatical behavior. Some final reflections raise questions for the overall Pentecostal Movement in Britain.