This chapter turns to the mathematics of medieval Islam. These include the mathematical theories and practices that grew, and often flourished, in that part of the world where the dominant religious and cultural influence was the religion of Islam, though this chapter focuses on the mathematics written in Spain and North Africa. The historical period under consideration is roughly the 700 years from 750 CE to 1450 CE, although the earliest mathematical works date from around 825. The chapter first discusses the arithmetic from this period, through the works of Aḥmad ibn al-Bannā, and others. Treatises on algebra, combinatorics, geometry, and trigonometry also follow, focusing on the selected works of many notable mathematicians of medieval Islam.