This paper investigates the interdisciplinary relations of nanotechnology (Nano), biotechnology (Bio), information technology (Info), and cognitive science (Cogno) (together known as NBIC converging technologies) using different bibliometric techniques. For each set of two (pairs) and three (trios) of subjects, overlaps in journal citation, authorship, publication journals, and keywords were calculated for all Iranian NBIC articles published from 2001 to 2015 in international journals. Maximum and minimum spanning trees were used to visualise the interdisciplinary relations. To determine the nature of convergence between the subjects, an expert panel categorised the shared keywords of each pair and trio of subjects using four categories of tools, material, applications and techniques. The results showed that overall the pairs of Nano–Bio and Nano–Info had the highest level of mutual interdisciplinary relations. Info–Bio and Cogno–Bio had the weakest mutual interdisciplinary relations. Among the trios, Nano–Info–Bio had the strongest relations and Cogno–Nano–Info had the weakest. The dominant type of convergence for Nano–Bio and Cogno–Bio was sharing materials. For Nano–Info the dominant type of convergence was sharing tools and techniques. For Info–Cogno, and Info–Bio sharing techniques was the dominant type of convergence, and for Nano–Cogno sharing materials and applications was most dominant. Nano–Info–Bio mostly shared materials and applications. Identifying weak and strong ties between the four NBIC fields can help plan for their further convergence at science and technology levels.