This thesis investigates the origins of the political and religious movement which developed within the New Model army between March 1647 and May 1649, by examining the preceding period (1644-1647) when the army was formed and began its activity. It tries to elucidate how an army, raised with strictly military aims and subjected to a particularly rigorous discipline, could develop representative structures (General Council, agitators) and constitutional programmes. As there is relatively little direct evidence concerning the army's religion and politics before 1647, I have analysed the influences to which the soldiers would have been subjected. Two main factors have been isolated, which contributed to the process of politicisation in the New Model. One concerns the army more directly and specifically: the propaganda addressed to soldiers by Parliament (newsbooks, declarations) army commanders and especially preachers. By instilling a sense of personal commitment to a cause and justifying resistance of subjects to their King, this propaganda encouraged the soldiers to think and decide for themselves. This, in turn, tended to conflict with the unquestioning obedience required by the military code. The other factor is more long-term and tends to involve English society at large. It is a complex of processes taking place in church and state on the eve and during the civil war. In both spheres a greater participation of common people in public affairs began to develop. The spreading of "gathered churches" and the campaign of popular petitions and demonstrations in 1640-1642 are the most significant examples. Finally, some attention has been paid to the early manifestations of a political or religious radical consciousness, in the New Model and other parliamentary armies. The experience of the latter may also have had an influence on Fairfax' s army.