The use of audio for instruction has a long history. For centuries, the spoken word was a principal method used in education. This changed in the mid-15th century with the invention of the printing press and the ability to reach large audiences through the distribution of books and other printed materials. While text remained a dominant medium in education for centuries (and still is currently), the invention in the latter half of the 19th century of the telephone, the phonograph, and the radio brought about an increase in the use of audio for instruction. Since this time, audio has continued to be an important instructional medium as audio production tools have become more readily available and easier to use.