The Bible records many different circumstances, types, and lengths of fasts. Joshua fasted forty days, and Daniel partially fasted twenty-one days. It is recorded that the apostly Paul was on at least two fasts; one for three days and one for fourteen days. Peter fasted three days, and, of course, we know that Jesus fasted forty days in the wilderness.
The three types of fasts found in the Scriptures are the absolute fast, the normal fast, and the partial fast. First, an absolute fast, is EXTREME and should only be done for very short periods of time. On an absolute fast, you take in nothing- no food or water. Depending on your health, this fast should be attempted only with medical consultation and supervision.
On a normal fast, you typically go without food of any kind for a certain number of days. You DO drink water, and PLENTY of it! Depending on the length of the noral fast, you may also choose to take clear broth and juice in order to maintain your strength.
And then there is the partial fast. A partial fast can be interpreted many ways. The way it cannot be interpreted is to include that time between about 11:00pm and 6:00 a.m.- when you are sleeping!  A partial fast usually involves giving up particular foods and drink for an extended period of time.
The most commonly used example of a partial fast is found in the Book of Daniel (ch10). Grieved over the plight of Israel, Daniel began to fast, taking no sweets, no meat, and no wine for three weeks, during which time he was focused in prayer. At the end, his prayer was answered by an angel! The duration of fasts can vary. There are significant numbers we find in the Bible, which include three days, seven days, twenty-one days, and forty days. But there are references to half-day fasts and twenty- four hour fasts as well.

As a church we are choosing to come together and corporately fast for forty days. This year's theme is "Restoration". Webster defines restore as: to come back to life, to bring back, to make new, to rebuild. What do you need God to restore in your life???

 (Reference: Jentezen Franklin- Fasting)

What is fasting? Stated simply, biblical fasting is refraining from food for a spiritual purpose. Fasting has always been a normal part of a relationship with God. As expressed by the impassioned plea of David in Psalm 42, fasting brings one into a deeper, more intimate and powerful relationship with the Lord. David was fasting. His hunger and thirst for God were greater than his natural desire for food. As a result, he reached a place where he could cry out from the depths of his spirit to the depths of God, even in the midst of his trial. Once you've experienced even a glimpse of that kind of intimacy with our God- our Father, the holy Creator of the universe- and the countless rewards and blessings that follow, your whole perspective will change.

In Matthew 6, Jesus provided the pattern by which each of us is to live as a child of God. That pattern addressed three specifics duties of a Christian: giving, praying, and fasting. Jesus said, "When you give..." and "When you pray..." and "When you fast...". He made it clear that fasting, like praying and giving was a normal part of Christian life. 
Solomon, when writing the books of wisdom for Israel, made the point that a cord, or rope, braided with three strands is not easily broken.  Likewise, when giving, praying, and fasting are practiced together in the life of a believer, it creates that type of threefold cord. (A threefold cord is not quickly broken.- Ecclesiastes 4:12)

Could we be missing our greatest breakthroughs because we fail to fast?

(Reference: Jentezen Franklin- Fasting)