The 70th Week of Daniel is an eschatological and prophetic term, often used to refer to the final seven years of this age, during much of which (especially the second half) there will be a great purging of the earth.  The concept of this seven-year period comes from (Daniel 9:27a).  In the Orthodox Jewish Bible, it reads this way:

And he shall confirm brit [covenant] with rabbim [the many] for one heptad [week of seven years]; and in the midst of the heptad he shall cause the zevach [sacrifice] and the minchah [gift offering] to cease, and on the kenaf [wing or overspreading] of the abominations is one making desolate, even until the complete destruction, a destruction that is decreed, shall be poured out upon the Shomem [Desolator, Destroyer]. (Daniel 9:27—OJB).

According to the angel Gabriel, by the end of 70 “weeks” of years (a “week” being equivalent to 7 years), it has been decreed by God, concerning Daniel’s “people” (Israel) and “holy city” (Jerusalem), that the following will come to pass (Daniel 9:24):

• all transgression would be finished or restrained,
• all sin would be put to an end,
• atonement would be made for all wickedness,
• everlasting righteousness would begin,
• all vision and prophecy would be sealed up, and
• the most Holy One [Jesus, the Christ] and most Holy Place would be anointed (see rule and reign and millennial Temple).

The final segment of the 70 “weeks,” of course, will be the “70th Week.”  This ultimate period of 7 years will commence with the confirmation or strengthening of a covenant, presumed to involve Israel and other unspecified nations or peoples, for one “week” or “heptad” of years—that is, for seven years (Daniel 9:27a).  Apparently, the agreement will be confirmed, affirmed, and/or supported by a man who is known in the Bible as the “man of lawlessness” (2 Thessalonians 2:3) or, more commonly, the “Antichrist.”

The exponential curve in the “Graph of the 70th Week” depicts the “Intensity of Troubles” on the earth, as a factor of “Time,” following the confirmation of the covenant for 7 years.  For 3˝ years after the establishment of the confirming agreement, worldwide deception, troubles, and sorrows (including more frequent, severe, and widespread earthquakes, plagues, famines and wars) will continue to increase gradually, just as the curve to the left of the vertical axis is more horizontal than vertical.

At the midpoint of the 70th Week, the abomination that causes desolation will be set up in what Jesus described as “the holy place” (Matthew 24:15).  Most have thought that this would be the Third Temple, yet to be built in Jerusalem.  However the word rendered as “temple,” in 2 Thessalonians 2:4 and in Revelation 11:1, is better translated “shrine.”  The Islamic Dome of the Rock, atop the Temple Mount, is both a holy place and a shrine.  Perhaps this will turn out to be the prophesied structure.

After this point, great tribulation, suffering, and cataclysms around the world will escalate markedly, just as the curve to the right of the vertical axis is more vertical than horizontal.  Severe calamities will soar, unabated, during the final 3˝ years of the 7-year period.

If not before Jesus returns, there will be another Temple after Jesus returns to earth.  He Himself will be in charge of constructing the millennial Temple.  This Temple probably will be dedicated 75 days after His return on Yom Kippur, and the latter will be 1,260 days after the midpoint of the 70th Week.  Each year, the beginning of Hanukkah is 75 days following Yom Kippur; so 1,260 days + 75 days = 2,335 days—fulfilling Daniel 12:12.  Since the ancient Second Temple was rededicated and consecrated during Hanukkah, it is reasonable to suppose that the same will be the case for the millenial Temple.

Now, God will be opposed to the 7-year accord, involving Israel, because His chosen people (the Israelites) will have entered into the agreement without having consulted Him and without having gained His approval.  This is shown in the Old Testament book of the prophet Isaiah (Isaiah 28:15-19, 57:8,9).  The Israelites will be relying on a man to protect them from their enemies, rather than looking to God  to guard and defend them.

Most Christians believe that, at some point during the 70th Week, The Rapture of believers will take place (see also Pre-Wrath Rapture).  I believe in secondary rapture events.  The timing of the momentous catching-up event(s) is a topic of considerable debate (see Views and Debates).

Many embrace the erroneous belief that they will be removed from the earth prior to the onset of the entire 70th Week (via the Pre-Tribulation Rapture).  Initially, they will not recognize that the final seven-year period of this age has begun, since they still will be present on the earth, anticipating the Rapture to take place.  As a result, once it has become unmistakably clear that the 70th Week already has commenced, many may believe that they have been “deceived” by their Christian leaders, and/or “abandoned” by Jesus, resulting in a great apostasy of believers.

A detailed, sequential description of the Book of Revelation can be found in this commentary: The Chronology of Revelation.  A chart can be found at The 70th Week and Extensions.  Yet another chart of The 70th Week and Extensions contains Bible passages referencing portions of the 70th Week.