Soul Society is known to be divided into two branches. They are known as the "East Branch" (東梢局, Tōshōkyoku; Literally meaning "Eastern Office"), which oversees Japan, and Soul Society West Branch (尸魂界・西梢局 (ソウル・ソサエティ ウエスト・ブランチ), Souru Sosaeti Uesuto Buranchi; Japanese for "Dead Spirit World Western Office"), which oversees London.
In ancient times, before the separation of Soul Society, the Material World, and Hueco Mundo, the universe existed in ambiguity and the cycle of souls in chaos. It remained this way for one hundred million years, until Hollows were introduced to the cycle and began to devour Humans, which slowed the circulation down. Eventually, many of these Hollows cannibalized one another, forming the first Menos. The universe reacted to the creation of such a being and gave way to the Soul King, who destroyed the Menos Grande and allowed the cycle of souls to resume.
Unfortunately, the Soul King's method of destroying Hollows (which very much resembled the Quincy) threw the cycle into further chaos. In response to this, five powerful individuals—those who were the ancestors of the Four Great Noble Families and an unknown fifth—rose in opposition to the Soul King's actions, each with their own motivations. Regardless of their varying motivations, these early nobles ultimately decided to split the world in three: a world of order, a world of implementation, and a paradise of sand for Hollows. But, in order to accomplish their vision, they needed the power of the Soul King.
The Shiba Family ancestor was the only one of the five to speak out against the plan, but they were soundly ignored. The Soul King was captured, hacked up, and his remains were restrained in a crystal. Then, his power, "The Almighty," was used as the keystone to create the three worlds: Soul Society, the Material World, and Hueco Mundo. Meanwhile, the pieces that were gouged out of the Soul King's body fell into the Material World and Soul Society. This became known as Soul Society's "original sin" (原罪, genzai).
200 years ago, Soul Society carried out a genocide of the Quincy in order to prevent them from unbalancing the world. When the surviving Quincy in the Material World were discovered, the Shinigami pleaded with them to stop their eradication of Hollows. However, not only did the Quincy refuse to stop, their numbers in the Material World increased. Most of the remaining Quincy in the Material World were killed during this genocide.
Soul Society and the Material World are on opposite sides of one another, with the Dangai and Hueco Mundo existing in the space between them. To access Soul Society, one uses a Senkaimon (穿界門; Literally meaning "World Penetration Gate") and a Hell Butterfly to guide them. Hollows and Arrancar can access Soul Society with a Garganta (黒腔 (ガルガンタ), Garuganta; Spanish for "Throat", Japanese for "Black Cavity").
Soul Society functions similarly to feudal Japan. The Shinigami live within the Seireitei, while the average Soul lives in the Rukongai. The districts closer to the Seireitei are generally more prosperous and the people there live in relative comfort. However, the outer districts are poverty and violence stricken. Despite this, souls (without spiritual power) will never go hungry. Families separated by death are rarely reunited in Soul Society and, therefore, souls cluster together and live in makeshift families of complete strangers.
Soul Society also has an aristocracy. The Four Great Noble Families occupy the Seireitei along with the Shinigami, as well as many minor noble families, and have considerable political clout within Soul Society's government.
Women are generally looked down upon in Soul Society and are not seen as typically being capable of climbing the ranks of the Gotei 13. It was said that Miyako Shiba, wife of well-respected Shinigami Kaien Shiba, struggled a great deal to climb the ranks because of her gender.
Though the Soul King is the official monarch of Soul Society, the Central 46 governs all of Soul Society. They adjudicate the law and pass sentences on criminals. It consists of forty elders and six judges whose orders and commands are absolute and are to be taken without question.