Interorganizational alliances are widely recognized as critical to product innovation. A notable trend is the rapid growth of new product development (NPD) alliances between large, well-established firms and small, growing firms. This dissertation is comprised of two studies on the formation and termination of asymmetric new product development alliances. In study one I examine the factors that drive the changes in shareholder values of the partner firms. I develop and empirically test a model of short-term changes in shareholder values of larger and smaller firms involved in NPD alliances, using the event study methodology on data covering 167 asymmetric alliances in the information technology and communication industries. The model accounts for selection correction, potential cross-correlation across the residuals from the models of firm value changes for the larger and smaller firms, and unobserved heterogeneity. The results suggest that both the partners experience significant short-term financial gains, but there are considerable asymmetries between the larger and smaller firms with regard to the effects of alliance, partner and firm characteristics on the gains of the partner firms. The findings of this study have important implications for managers of both large and small firms. In study two I develop and test a framework of the determinants of new product alliance (NPA) terminations. The hypotheses for study two are tested on a unique database comprised of 401 new product alliances involving 24 pharmaceutical firms during 1990-2005. NPA terminations are modeled using Cox's proportional hazard specification that accounts for the unobserved heterogeneity of firms with multiple NPAs, competing risks and ties among NPA duration times. The results suggest that NPA terminations are not made in isolation but are influenced by composition of the firm's portfolio. The results also suggest that NPA terminations are predicted to a great extent by competition between alliances (i.e., product market rivalry) and competition within alliances (i.e., partner value). The findings of this study have important implications for managing a portfolio of new product partnerships.