Heaven

Heaven, a place created by God, intended to be the home-realm of Angels, is an ageless, ethereal, and divine realm. It serves as a dwelling place and a base of operations for angels, and is a final resting place of worthy deceased souls. Although many people--both good and evil, Christian and non-Christian alike--have made their way to Heaven, making the exact requirements to go to Heaven unclear.

God resided in Heaven with his angels until his departure sometime in the distant past. In God's absence, the archangel Michael led the angelic Host and directed the affairs of Heaven. Raphael was also an authority. The appearance of angels in Heaven is not necessarily human, though they usually stay in their vessel, as it isn't always easy to find a suitable vessel for angels. For example, Zachariah says that in Heaven, he has six wings and four faces. Angels draw some of their powers - demonic exorcism, healing and possibly resurrection - from Heaven. Those who fall and are "cut-off" from Heaven are weakened, and are not allowed to return on their own. It is still possible for the banished to communicate with Heaven. Anna can hear other angels speaking, even without her grace. Castiel is able to communicate with Sam and Dean through a link to electronic equipment - such as a radio or TV - in their memories.

Heaven also serves as a destination for deserving human souls after death. They occupy the happy memories they experienced on Earth, reliving them in their personal Heavens. It is unknown how a human soul is allowed salvation in Heaven. Joshua suggests that it is on a case-by-case basis and can be God's decision; this is the case with Sam and Dean. Raphael says that if a person is devout enough, it can trumps all sins (which is why the disgraced Enron executive Ken Lay got into Heaven).

Foundation and History
The center of Heaven is called The Garden (Zachariah refers to it as "Mission Control"), and, like the rest of the realms, each person sees it how they want to. The Garden can be reached by the Axis Mundi, which is often seen as a river or a road, depending on the person.

Most demons fear Heaven's inhabitants, God and his angels, and will flee from them on sight. Some of the more powerful demons like Alastair, can send angels back to Heaven, but only someone with an angel or archangel's sword, God, or Death, can kill an angel. Despite the fact that Uriel states that only an angel can kill another angel, Zachariah is killed with an Angel sword or dagger used by Dean. At one point God was in Heaven; this was when he sent Castiel to Hell to save Dean Winchester, but for some unknown reason, left Heaven afterwards and still hasn't returned. According to Joshua, God is walking the Earth and is not interested in helping the Winchesters stop the Apocalypse.

Since God's abandonment of Heaven, Michael is assumed to have taken command as his right as "Viceroy of Heaven" with some assistance from his younger brother, Raphael. After Michael was trapped in Lucifer's Cage, Raphael took over, leading it like a dictatorship. When he announced his plans to free Michael and Lucifer and restart the Apocalypse, Castiel opposed him. This resulted in a civil war between Raphael's forces and Castiel's followers. The war ended when Castiel absorbed all the souls of Purgatory and destroyed Raphael and his followers. He then declared himself God and took control of Heaven. However, he then disappeared and was presumed dead, and Heaven once again fell into disarray.

In the aftermath of Castiel's disappearance, Hester, who was once part of Castiel's garrison, took command of the remaining Angels. She was assisted by Inias, also an Angel from Castiel's garrison. In the wake of Hester's death in Reading Is Fundamental, it is unclear who is now leading Heaven. It is possible that Inias is now in charge, as he is seen commanding the Angels to take the Prophet Kevin back home at the end of the episode.

Hierarchy
Heaven's armies are divided into garrisons charged with specific tasks. Castiel's garrison, for example, was assigned to watch and protect the Earth. Each garrison is led by a Captain (before his rebellion, Castiel was Captain of his garrison). Garrison Captains report to Seraphs, such as Zachariah, who in turn answer to the Archangels themselves. In God's absence, the Archangels are the highest order of authority in Heaven.

Heaven's hierarchy is extremely strict. All Angels are expected to obey orders from their superiors without question. Emotions are highly discouraged amongst Angels, as many of the higher ranking Angels see them as doorways to doubt. Disobedience or lack of faith is punishable by demotion, banishment, torture, and even death.

It should be noted that not all angels are warriors. Some have other tasks, such as being scribes (Metatron) and gardeners (Joshua).

Trivia

 * Ash tells the brothers that Heaven is comprised of many places, like 100 billion individual Heavens. Dean then states that everyone gets a piece of paradise, thus hinting to that Heaven is infinite. This also means that in the Supernatural universe, religion is not an important deciding factor for who gets in to Heaven when they die.
 * Atropos is the only non-Angelic being or revived human to go to Heaven and return.

Season 5

 * Dark Side of the Moon

Season 6

 * The Man Who Would Be King

Season 7

 * Meet The New Boss