What is behind multiple institutional affiliations in academia?

Multiple institutional affiliations (or co-affiliations) occur when an academic belongs to more than one organisation. Recent research shows an increase in academics with multiple affiliations, but evidence on how these are organised and on academics' motivations is mainly anecdotal. In this study we develop a typology of co-affiliations, which identifies four types based on their purpose and origin. We draw on results from a unique international survey of academics in three major science nations (the UK, Germany, and Japan) to study the different factors that could explain the four types of co-affiliations. The analysis shows that academics' motivations (networking/prestige, resources, teaching, or personal income) correlate with the observed co-affiliation type. Researcher-initiated and research-focussed co-affiliations are often motivated by networking and resource access while co-affiliations that serve other than research purposes are more often income-motivated.