Darparu gwybodaeth, cyngor a chymorth mewn perthynas â threthi Cymru i Weinidogion Cymru a threthdalwyr;Ymdrin â chwynion ac anghydfodau trethdalwyr;Hyrwyddo cydymffurfiaeth o ran trethi;Amddiffyn rhag achosion o efadu trethi ac osgoi trethi; aChefnogi'r gwaith o ddatblygu polisi trethi Llywodraeth Cymru.
Provide information, advice and assistance about Welsh taxes to Welsh Ministers and taxpayers;Resolve taxpayer complaints and disputes;Promote tax compliance;Protect against tax evasion and tax avoidance; andSupport the development of Welsh Government tax policy.