Informal advisory networks structure the flow of knowledge and fundamentally influence the success of innovation attempts. Philip Roth analyzes the development of such networks. In addition to partner selection decisions, opportunity structures have proven to be particularly significant. While partner selection decisions can now be explained in a differentiated manner, it has not yet been possible to empirically elucidate the systematic effect of opportunities. Based on innovative conceptual and methodological groundwork, the author succeeds for the first time in explaining in detail how opportunity structures operate. The empirical analysis of processes in three research and development departments highlights the conditions under which encounters lead to informal professional exchanges and demonstrates that these conditions can vary between local cultures.