Supply chain flexibility has become an important ingredient to remain competitive in today's increasingly complex business environment. Within this context, drawing from the knowledge-based view of the firm, we investigate the influence of internal and external knowledge transfer activities on supply chain flexibility. In addition, taking a contingency perspective, we hypothesize about the moderating effects of product and supply complexity on the relationships between knowledge transfer and supply chain flexibility. We test our hypotheses with data collected from procurement and supply chain professionals in Germany. Pursuant to our expectations, we find a positive and significant influence of internal and external knowledge transfer on supply chain flexibility. We further confirm a negative moderating effect of supply complexity on the relationship between internal knowledge transfer and supply chain flexibility, and a negative moderating effect of product complexity on the relationship between external knowledge transfer and supply chain flexibility. However, contrary to our expectations, we find significant positive effects for the remaining two moderations, being indicative of the unique dynamics emanating from complexity, able to yield both negative and positive moderation effects contingent on the situation. Overall, these findings provide important insight into the value of knowledge transfer activities for supply chain flexibility, and especially into when knowledge transfer is most effective, drawing attention to influential complexity contingencies. Theoretical and practical contributions are discussed.