We propose an extension of action theories to intention theories in the framework of situation calculus. Moreover the method for implementing action theories is adapted to consider the new components. The intention theories take account of the BDI (Belief-Desire-Intention) architecture. In order to avoid the computational complexity of theorem proving in modal logic, we explore an alternative approach that introduces the notions of belief, goal and intention fluents together with their associated successor state axioms. Hence, under certain conditions, reasoning about the BDI change is computationally similar to reasoning about ordinary fluent change. This approach can be implemented using declarative programming.16 page(s