The Thieves Guild is a criminal network found in the Western Kingdoms.
The Thieves Guild's activities include extortion, bribery, smuggling, murder, and all manner of illicit activities. They go to great lengths to keep their inner workings a mystery to outsiders, which includes masking its leadership. It usually recruits its members from poverty-stricken slums. Initiates train in pickpocketing, and those who show promise ascend in rank, akin to how a craftsman would ascend in a trade guild. Ascending the ladder of the guild's heirarchy guarantees an individual dangerous, but lucrative work.
The Thieves Guild arose in the years after Rakkis founded the nation of Westmarch. Since that time, the Guild has spread to cities throughout the kingdom and beyond. By the 13th century it had a presence in Kingsport. Members of the guild were present in Westmarch's capital during the Reapers' invasion.