The Great Disappointment in the Millerite movement was the reaction that followed Baptist preacher William Miller's proclamation that Jesus Christ would return to the Earth by 1844, which he called the Second Advent. His study of the Daniel 8 prophecy during the Second Great Awakening led him to conclude that Daniel's "cleansing of the sanctuary" was cleansing the world from sin when Christ would come, and he and many others prepared. When Jesus did not appear by October 22, 1844, Miller and his followers were disappointed.

These events paved the way for the Adventists who formed the Seventh-day Adventist Church. They contended that what had happened on October 22 was not Jesus's return, as Miller had thought, but the start of Jesus's final work of atonement, the cleansing in the heavenly sanctuary, leading up to the Second Coming.

Between 1831 and 1844, on the basis of his study of the Bible, and particularly the prophecy of Daniel 8:14—"Unto two thousand and three hundred days; then shall the sanctuary be cleansed"—William Miller, a rural New York farmer and Baptist lay preacher, predicted and preached the return of Jesus Christ to the earth. Miller's teachings form the theological foundation of Seventh-day Adventism. Four topics were especially important:

Miller's approach was thorough and methodical, intensive and extensive. His central principle for interpreting the Bible was that "all scripture is necessary" and that no part should be bypassed. To understand a doctrine, Miller said one needed to "bring all scriptures together on the subject you wish to know; then let every word have its proper influence, and if you can form your theory without a contradiction you cannot be in error." He held that the Bible should be its own expositor. By comparing scripture with scripture, a person could unlock the meaning of the Bible. In that way the Bible became a person's authority, whereas if a creed of other individuals or their writings served as the basis of authority, then that external authority became central rather than the teaching of the Bible itself. Miller's guidelines concerning the interpretation of Bible prophecy was built upon the same concepts set forth in his general rules. The Bible, so far as Miller and his followers were concerned, was the supreme authority in all matters of faith and doctrine.

The Millerite movement was primarily concerned with the return of Jesus, literally, visually, in the clouds of heaven. The French Revolution was one of several factors that caused many Bible students around the world who shared Miller's concerns to delve into the time prophecies of Daniel using the historicist methodology of interpretation. They concluded, to their satisfaction, that the end of the 1,260-"day" prophecy of Daniel 7:25 in 1798 started the era of "time of the end". They next considered the 2,300 "days" of Daniel 8:14.

There were three things that Miller determined about this text:

Miller tied the 2,300-day vision to the Prophecy of Seventy Weeks in Daniel 9 where a beginning date is given. He concluded that the 70 weeks (or 70 sevens, or 490 days) were the first 490 years of the 2,300 years. The 490 years were to begin with the command to rebuild and restore Jerusalem. The Bible records four decrees concerning Jerusalem after the Babylonian captivity:

The decree by Artaxerxes empowered Ezra to ordain laws and to set up magistrates and judges for the restored Jewish state. It also gave him unlimited funds to rebuild whatever he wanted at Jerusalem.