This book provides a full listing of the troop and company commanders who served in the New Model Army during the first four years of its existence. A second volume covering the final years of the army's existence is currently very close to completion. It will be published during 2016. This is the first time that the officer corps of the New Model Army has been pieced together on such a scale and with such an extensive range of source materials. Unsurprisingly it corrects numerous errors to be found in more general histories of the army. The book is therefore an essential tool for studying the officer corps of the first English army in which social status was not the prime prerequisite for attaining a senior military rank. Additionally, it is fully indexed and referenced. This will allow readers, whether military historians, local historians or family historians, to progress their particular interests through further exploration of archival and printed sources. In part one the data concerning the careers of troop and company commanders is presented in the form of snapshots of the army taken on six occasions between April 1645 and May 1649. However, the information to be found in the very extensive footnotes will enable the reader to create a highly accurate reconstruction of the names of the troop and company commanders at any date in that period. In part two a similar exercise is conducted with respect to the junior commissioned officers. In their case the surviving documentary evidence makes a complete reconstruction impossible. It is, however, important that their names are recorded as considerable numbers went on to serve as troop and company commanders, and indeed field officers and colonels, during the last ten years of the New Model Army's existence. Finally, in appendix one regimental lists are presented for the first time of the Earl of Essex's army at the time of its incorporation into the New Model Army, thus complementing the work of Laurence Spring on the New Model's other two progenitors, the armies of the Earl of Manchester and Sir William Waller. The book is not a new history of the New Model Army, but it does include chapters on topics that are not addressed head-on in Ian Gentles, The New Model Army 1645-1653 (1992). One examines the extent to which the New Model Army was an English Army, an issue first raised by Mark Stoyle in Soldiers and Strangers (Yale, 2005). Another discusses the positions held by the officers before they became troop or company commanders in the New Model Army, and the effect this may have had on their subsequent military careers. A third explores the circumstances under which officers left the army in the period 1645-1649, whist a fourth questions the notion of pinning numbers to the New Model Army regiments as was the practice in the British Army of the late eighteenth and nineteenth centuries.