In this paper, we consider a framework of optimal growth, in which technology and tastes are changing over time. The model is an aggregative one, and follows closely those studied by Brock [1971] and Brock and Gale [1969]. In this framework, we address two important issues in the area of optimal intertemporal allocation of resources. First, we provide of weakly maximal and optimal programs. (Weak-maximality and Optimality are defined, following the approach of Brock [1970] and Gale [1967] respectively, in Section 2). Second, we provide stability of weaklymaximal and optimal programs. Price characterizations are of importance since they imply that socially desirable allocations can be attained by decentralized maximizing decision making of firms and consumers,2 (the decentralization being accomplished through a pricesystem), provided an appropriate on asymptotic behavior of input-values3 is satisfied. In the literature, it is this additional condition which has not been precisely characterized in a model with changing technology and tastes. To find this condition, we have found it useful to draw on the results obtained in the theory of efficient allocation of resources, which deals with a similar problem of price characterization of efficient programs. For weakly-maximal programs the appropriate is that the reciprocal of the input-values should not be summable (Theorem 3.1). For optimal programs, the input-values should be uniformly bounded (Theorems 4.1 and 4.2). The results of Brock [1971], and Benveniste and Gale [1975] are particularly important in obtaining these results. It should be noted that criteria for the existence of optimal programs in various particular cases of our framework have been given by Mirrlees [1967], Phelps [1966], and Inagaki [1970]. A unified elegant treatment of this question is given in Brock and Gale [1969]. Consequently, we do not address this issue in our paper. The asymptotic stability properties of weakly-maximal and optimal programs