Dispensationalism is considered controversial in some sectors of Christendom, however, it is often misunderstood. This Theology suggests that at the turn of each of these 7 time periods, God uses a new and fresh system of communicating and dealing with His people. ‘God never changes’ refers to His Character and is in no way a reference to His Divine Ordinances.

Moreover, these time periods, known as dispensations, unveil the entire plan of salvation and show that God has a 7,000 year plan for mankind.

Overview: The 7 Dispensations God Has Ordained & Instituted:

1). Innocence—This period lasted from the moment of Creation to the Fall of Man. (Genesis 1:28-30 & 2:15-17 & Genesis 3) At this time, there was no sin on earth, as the world was in a period that preceded sin and wickedness, when God dealt directly with man because man was in a time of innocence. (This period lasted only around 1 week.)

2). Conscience—From the time period that Adam and Eve were expelled from the Garden until the wickedness of mankind got so bad that God took out the world with a flood. God dealt with man by allowing the people to govern themselves via their own will and conscience, however, He was still very much involved in their lives. (Genesis 3:8-8:22, 6:1-6 & 11-18) (Spanned a period of around 1,700 years)

3). Human Government—God instituted the dispensation of human government from the time after the flood until the tower of Babel. God Commanded Noah and his sons to repopulate the earth and allowed them to use meat for food. However, they did not obey God and populate the earth because they were preoccupied with their own desires and sought after ways to live without God’s Sovereignty, therefore, God confused their languages. (Genesis 8:1-9:7 & Genesis 11:1-9) (This period lasted around 429 years.)

4). Promise—This time period began at the time God called Abraham. The call of Abraham, "the lives of the patriarchs, and the enslavement of the Jewish people to Egypt all fall under the dispensation of promise and ended with the Jews Exodus from Egypt.” (compellingtruth.org) During this period God dealt with man through His Grace and Mercy until the wickedness of Israel exceeded His Patience.(Genesis 12:1-7) (Lasted around 430 years)

5). Law --This was the time period where God dealt with His people through the Law. It began with the delivery of the 10 Commandments and ended with the Crucifixion of Christ. “The Law outlined the standard of perfection that God required from His people, and included the instructions about temple worship and sacrifices. This was the age of priests, prophets and kings, both good and evil.” (compellingtruth.org) (Exodus 19-23) (Spanned a period of around 1,500 years) 

6). Grace—This dispensation is that of the Church Age or the Age of Grace; the one we are currently living under. It started at the Resurrection of Christ and will go on until the Rapture of the church. During this time period believers are saved through faith in Christ. God’s Mercy is on those who believe on HIM. (Luke 22:20, Daniel 12:1-4, Matthew 24:21-27, Daniel 9:24) During the 7 years of tribulation on the earth, God will not be dealing with the people, but leaving them to their own devices. (Will span a period of around 2,000 years.)

"Seek the LORD while He may be found, Call upon Him while He is near." (Isaiah 55:6)

7). Kingdom—The Millennial kingdom starts with Satan’s defeat and goes on for 1,000 years. And in this Glorious time period, God will put an end to all sin and death. And Christ Jesus will Reign with His saints and there will be Perfect Peace on the earth, like God intended in the Garden. (Revelation 20:1-4 & Revelation 21 & 22)

“And God will wipe away every tear from their eyes; there shall be no more death, nor sorrow, nor crying. There shall be no more pain, for the former things have passed away.” (Revelation 21:4)

NOTE: As for the 7 year tribulation, it doesn't appear that theologians have identified that period as fitting into any dispensation, not the end of the church age, or as dispensation number 8! Either of these fit seamlessly, as "the number 7 is the number of spiritual; divine fullness, completeness and totality."  perfection and 8 symbolizes resurrection and a new beginning." (Taken from turnbacktogod.com)

NKJV

The seven dispensations – What are they? (compellingtruth.org)