Mixed-sex education, also known as mixed-gender education, co-education, or coeducation (abbreviated to co-ed or coed), is a system of education where males and females are educated together. Whereas single-sex education was more common up to the 19th century, mixed-sex education has since become standard in many cultures, particularly in Western countries. Single-sex education, however, remains prevalent in many Muslim countries. The relative merits of both systems have been the subject of debate.