The four books is a collection of confucian root texts. It has been established that none of them has been written by Confucious (K’ung-tzu, 551-479 B.C.E.) but rather compiled by his students after his dead. However, The four books, are considered the closest we come to the original teaching of Confucious. If you were to seek a position in the Chinese empire you would have to pass a civil service exmination, that required that you had read the four books.
The collection consists of the works: Confucian Analects, The great learning, The doctrine of the mean, and The works of Mencius. This edition has both the original Chinese text and the English translation. This edition was translated and edited by James Legge. Download the book here (41 MB / 603 pages):