In 1526, the army of the Hungarian kingdom was soundly defeated by the army of the Ottoman sultan, Suleiman the Magnificent, in the battle of Mohács. In the following decades the lands that were once part of the Hungarian Crown were divided. On the eastern half of the former Hungarian kingdom a new state was born, the Principality of Transylvania. For one and a half century (1541-1691), Transylvania was a distinct state on European maps, and played an important military and strategic role in the struggle between the Ottomans and the Habsburgs in Central and South-East Europe. This book follows the efforts of the Transylvanian rulers to organise and to defend their new state, during its first seven decades of existence (1541-1613). The army at their disposal inherited an essentially medieval structure that reflected the social composition of the region. The bulk of the army consisted of the so called "county flags" (noble levies and conscripted peasants from their estates), the Székely levies (troops recruited in the districts of South-East Transylvania) and the troops supplied by the Saxon districts from the highly urbanised southern parts of Transylvania. In addition, the Transylvanian army also had several groups of professional soldiers that performed permanent or semi-permanent military service: the court guard (aule milites), the garrisons of the main fortifications concentrated on the western frontier of the principality and other groups that performed military service in exchange for tax exemptions like the riflemen (pixidari, pu?ca?i, puskások) and the guardsmen (darabontok, daraban?i). The last chapter of the book is focused on the main military campaigns in which the Transylvanian army was involved (the expedition of Giovanni Battista Castaldo in Transylvania and the Banat region 1551-1553, the "Fortress War" period 1552-1571, the Long Turkish War 1591-1606, etc.), with extensive descriptions of some of the most important pitched battles and sieges.Between 1541 and 1613, Transylvanian armies underwent a process of transition and adaptation that combined medieval traditions and early modern military innovations. AUTHOR: Dr. Florin Nicolae Ardelean (born in 1983), is a researcher at Babe?-Bolyai University in Cluj-Napoca, Romania. During his 14 years of work in the field of historical research, Dr. Ardelean has been involved in three national research grants, has published one monograph (in Romanian) and over 25 articles in academic journals (in Romanian and English) on the topics of late medieval and early modern warfare. His publications are based on research conducted in Romanian, Hungarian and Austrian archives and libraries. His professional experience also includes history teaching, various projects of historical popularisation and consultancy in the video game industry. 19 b/w ills, 8 colour plates, 5 maps, 1 table