Alliance formation is often described as a mechanism used by firms to increase voluntary knowledge transfers. Access to external knowledge has been increasingly recognized as a main source of a firm's innovativeness. A phenomenon that has recently emerged is alliance portfolio complexity. In line with recent studies this article develops a measure of portfolio complexity in technology partnerships in terms of diversity of elements of the alliance portfolio with which a firm must interact. The analysis considers an alliance portfolio that includes different partnership types (competitor, customer, supplier, and university and research center). So far factors that determine portfolio complexity and its impact on technological performance of f...