In a mixture experiment, several components are mixed to produce a response. The total amount of the mixture is a constant. Existing literature on mixture designs ignores the order of addition of the mixture components. In this presentation, we will discuss the the Order-of-Addition (OofA) mixture experiment, where the response depends on both the mixture proportions of components and their order of addition.  Full Mixture OofA designs will be shown, which ensure orthogonality between mixture model terms and addition order effects. These designs allow for the estimation of (1) typical mixture model parameters and (2) order-of-addition effects. Empirical results suggest that if mixture-order interactions are present, then the optimal proportions suggested by traditional mixture models may be misleading. Moreover, models which include both main effects and key mixture-order interactions are introduced. An application of these models to combinatorial drug therapy is provided, in addition to a simulation study.