Addressing the military organisation of both Royalists and Parliamentarians, the subject of this thesis is an examination of war effort during the mid-seventeenth century English Civil Wars by taking the example of Shropshire. The county was contested during the First Civil War of 1642-6 and also saw armed conflict on a smaller scale during the Second Civil War of 1648. This detailed study provides a comprehensive bipartisan analysis of military endeavour, in terms of organisation and of the engagements fought. Drawing on numerous primary sources, it explores: leadership and administration; recruitment and the armed forces; military finance; supply and logistics; and the nature and conduct of the fighting. The extent of military activity in Shropshire is explained for the first time, informing the history of the conflict there while reflecting on the nature of warfare across Civil War England. It shows how local Royalist and Parliamentarian activists and 'outsider' leaders provided direction, while the populace widely was involved in the administrative and material tasks of war effort. The war in Shropshire was mainly fought between the opposing county-based forces, but with considerable external military support. Similarly, fiscal and military assets were obtained locally and from much further afield. Attritional war in Shropshire from 1643 to 1646 involved the occupying Royalists engaging Parliamentarian inroads, in fighting the garrison warfare characteristic of the period. Although the outcome of both wars in Shropshire was determined by wider national events, in 1646 and again in 1648 the defeat of the county Royalists was due largely to their local Parliamentarian adversaries. Broadening this study to 1648 has provided insight into Parliamentarian county administration during the short interwar period.