William III Taillefer (also spelled Tallefer or Tallifer; c. 970 – September 1037) was the Count of Toulouse, Albi, and Quercy, as well as the Marquis of Gothie from 972 or 978 to his death.

[1] However, recent research has revealed that William was instead the son of Adelais of Anjou, known to have married a Raymond, "Prince of Gothia".

This discovery has required a complete reevaluation of the succession to the County of Toulouse during this period, and no new scholarly consensus has emerged.

William became the most powerful prince in western Languedoc and he saw the rise of the House of Capet in France and a corresponding decrease in royal authority recognised in the south.

His power did not remain undiminished in his own city of Toulouse, where he was forced by a council of local noblemen and clerics to give up dues imposed on the market there.