Research collaborations between universities and industry (U-I) are considered to be one important channel of potential localised knowledge spillovers. These collaborations favour both intended and unintended flows of knowledge and facilitate learning processes between partners from different organisations. Despite the copious literature on localised knowledge spillovers, still little is known about the factors driving the formation of U-I research collaborations and, in particular, about the role that geographical proximity plays in the establishment of such relationships. Using collaborative research grants between universities and business firms awarded by the UK Engineering and Physical Sciences Research Council (EPSRC), in this paper we disentangle some of the conditions under which different kinds of proximity contribute to the formation of U-I research collaborations, focussing in particular on technological complementarity among the firms participating in such partnerships.