The Jade Sea is east of the Summer Sea and south of Essos. It is divided from the Summer Sea by the large island Great Moraq, the Cinnamon Straits, and the Jade Gates with the isle of Qal. Also near the Jade Gates are the southern reaches of the Bone Mountains.
Yi Ti is in a forested stretch along the northern Jade Sea, and the Shadow Lands are to the east. The eastern Jade Sea transitions into the Saffron Straits, which separate the Shadow Lands in eastern Essos from Ulthos. It is unknown how much of the Jade Sea borders Sothoryos to the southwest.
Aside from Great Moraq and Qal, other islands in the Jade Sea include the Isle of Whips in the northwest, the Isle of Elephants in the southwest, Marahai in the center, Leng in the northeast, and the Manticore Isles in the southeast.
There are several cities along the Jade Sea, such as Port Moraq on Great Moraq and Zabhad on the Isle of Elephants. The island of Leng contains Leng Ma, Leng Yi, and Turrani. Mainland Essos includes Asabhad, Yin and Jinqi in Yi Ti, and Asshai at the tip of the Shadow Lands peninsula.
Aside from merchant traders, few from Westeros visit the area and they know little about it, except that Asshai and the cities of Yi Ti are on its far shores. The Jade Sea is considered an exotic name evoking fable, myth and adventure to those in Westeros. Past Yi Ti, on its eastern shores somewhere, is supposed to be a legendary dreaming city of poets.
It takes roughly two years to travel from Pentos to the Jade Sea and back in the best conditions. There is a traders' route that carries sea-traders around the Jade Sea. Because of the prevailing winds' direction, the route moves clockwise, beginning at the Jade Gates. From Qarth it goes east to Yi Ti, including Asabhad and Yin, then Leng, and possibly Asshai. Zabhad and Port Moraq are visited on the southern return leg of the route. The western shore of Great Moraq south of Qarth is also involved in the Jade Sea's trade.
A Game of Thrones
Before Khal Drogo's body is burnt on his funeral pyre Ser Jorah Mormont begs Daenerys Targaryen to come east with him, to Yi Ti, Qarth, the Jade Sea and Asshai by the shadow, to see all the wonders yet unseen. 
A Clash of Kings
In Qarth, Xaro Xhoan Daxos tries to entreat Daenerys to accompany him on his pleasure barge to go in search of a golden vintage of wine that is made across the Jade Sea. He also suggests that they journey around Yi Ti to search for the dreaming city of poets, to sip the wine of wisdom from a dead man's skull.
A Storm of Swords
A Feast for Crows
Before departing the Wall, Samwell Tarly overhears Maester Aemon tell Jon Snow that he left a book for him in his chambers, the Jade Compendium written by the Volantene adventurer Colloquo Votar, who traveled east and visited all the lands of the Jade Sea. He tells Jon there is a passage he might find interesting.
A Dance with Dragons
Illyrio Mopatis tells Tyrion Lannister of the Treasure, a Braavosi trading galley that once returned from the Jade Sea with cloves and saffron, jet and jade, scarlet samite and green silk … and the grey death.
In Volantis, when discussing how to find a Westerosi ship heading to Meereen, Quentyn Martell remarks that few come as far as Volantis and those who do fill their holds with silk, and spice from the Jade Sea, then bend their oars for home.
In Deepwood Motte Tristifer Botley suggests to Asha Greyjoy that they make new lives upon the sea as traders. They can voyage east and come back with silks and spices, as one voyage to the Jade Sea would make them very wealthy.
One voyage to the Jade Sea and we'll be as rich as gods.
- The Lands of Ice and Fire, "The East"
- A Game of Thrones, Chapter 3, Daenerys I.
- A Clash of Kings, Chapter 40, Daenerys III.
- A Dance with Dragons, Chapter 5, Tyrion II.
- A Clash of Kings, Chapter 27, Daenerys II.
- A World of Ice and Fire
- A Game of Thrones, Chapter 72, Daenerys X.
- A Storm of Swords, Chapter 71, Daenerys VI.
- A Storm of Swords, Chapter 19, Tyrion III.
- A Feast for Crows, Chapter 5, Samwell I.
- A Dance with Dragons, Chapter 6, The Merchant's Man.
- A Dance with Dragons, Chapter 26, The Wayward Bride.