We associate “crusaders” with the medieval world and those who took part in military campaigns during the period 1095–1291, the “golden age of crusading.” This chapter examines why groups of men and women throughout history have been described as “crusaders.” For many historians, “crusaders” are not just those who fought against Muslims, but those who took part in papally inspired campaigns in various theatres-of-war against diverse enemies, for which they took vows and enjoyed special privileges. We further use the word “crusader” to describe those whom popes encouraged to take part in military ventures, for example against the Ottomans, over a much wider chronological period – from the fourteenth to the nineteenth centuries. In modern times, crusade rhetoric has also been a key feature of both Western and Eastern religious and political discourse. Hence the chapter explores how our idea of “crusaders” has developed since the original use of the word.