The recent developments towards more systemic conceptualizations of innovation dynamics and related policies highlight the need for indicators that mirror the dynamics involved. In this contribution, we assess the role that 'non-patent references', found in patent documents, can play in this respect. After examining the occurrence of these references in the USPTO and EPO patent systems, their precise nature is delineated by means of a content analysis of two samples of nonpatent references (n=10,000). Our findings reveal that citations in patents allow developing nontrivial and robust indicators. The majority of all non-patent references are journal references, which provide ample possibilities for large-scale analyses focusing on the extent to which technological developments are situated within the vicinity of scientific knowledge. Application areas, limitations and directions for future research are discussed.