Ans: DTAA has four models: OECD model tax convention - This model is based on the residence principle.  UN model double taxation convention - This model is a combination of the source and residence principles. However, the key emphasis is given to the source principle.  US model income tax convention - Any country entering into DTAA with the USA must follow this model.  Andean community income and capital tax convention - South American member countries like Bolivia, Peru, Chile, Ecuador, and Columbia follow this model.