This article responds to recent calls by geographers for more critical, non‐essentialist and flexible conceptualisations of diaspora by developing the notion of an ‘elective diaspora’. This concept is elaborated using the case study of a specific knowledge diaspora, namely visiting researchers from the USA in the Federal Republic of Germany (FRG), who were funded by the Alexander von Humboldt Foundation, a research agency re‐established by the FRG in 1953. The analysis shows how the Humboldt programmes for transnational academic mobility and collaboration drew disproportionately on US‐based academics with biographical ties to German‐speaking central Europe, which has contributed to the proliferation of US–German knowledge networks in the post‐war period and prompts us to reconsider existing notions of diaspora in two ways. First, we emphasise the nuances of the researchers' emotional attachment to German language and culture. We point out that this cannot only be caused by biographical ties through birth and ancestry but also by other family relations, partnerships, friendships, work/living experiences, language skills and cultural knowledge. Second, we stress the elective nature of diasporic identities and belonging by emphasising that individuals can choose whether they wish to support diasporic networks of one or more communities and cultures they feel connected to. We suggest that this civic rather than ‘ethno’‐territorial understanding of diasporic networks has wider relevance for theorisations of diaspora, for studies of transnational mobility and knowledge transfer, and for university and public policies seeking to attract talent from abroad.