Motivated by the proliferation of multifunction products, we investigate product portfolio decisions of a single firm by analyzing the impact of three ma;'or factors. First, because multifunction products provide complete or partial functionalities of single-function products, we incorporate substitution or cannibalization effects between the potential products. Second, we explicitly model the variable costs of manufacturing the single0function and multifunction products. Third, we examine the firm's pricing decisions because of their impact on the degree of cannibalization between the multifunction product and one or more single-function products. Using an economic model, we first characterize the firm's optimal product portfolio (through a quantity-based decision), which in turn determines the market equilibrium prices for each product in its portfolio. Some of the unique insights stemming from our analysis are: (a) the optimal product portfolio choice is driven primarily by maximum profit margins for the single-function products weighted by the demand substitution effects; and (b) from a product design perspective, the complete functionality of the base single-function product is always included in the optimal product offering, but this is not necessarily the case with the complete functionality of the non-base single-function product.