It is only in the last 150 years that most people have been able to read and write in Europe and North America. In many other parts of the world this did not happen until the 20th century. Until then, literacy was mainly for clerics, that is, people who had training as priests. Even wealthy people were often illiterate, and used scribes to write for them. The invention of printing came before mass literacy. Before 1500, each book had to be created by hand, so there were few books available compared to the billions in the world today. Mass literacy needed cheap books.