The International Conference on Scientometrics and Informetrics in Leuven on 12–15 July 2021 was organised by KU Leuven in close collaboration with the University of Antwerp under the auspices of ISSI—the International Society for Scientometrics and Informetrics. It was the 18th meeting of a biennial conference series, which started in Belgium in 1987 and just came back to Belgium last year. The meetings before were organized in Canada (1989), India (1991), Germany (1993), and after the Society has been founded in 1993, in the USA (1995), Israel (1997), Mexico (1999), Australia (2001), China (2003), Sweden (2005), Spain (2007), South Africa (2009), Austria (2013), Turkey (2015), China (2017) and Italy (2019). However, due to the continuing constraints imposed by the COVID-19 pandemic and the resulting risks for organising a conference with physical presence of all attendees, the organisers decided to still go virtual in 2021. The organisation of this event proved a long and winding road paved with more challenges than originally expected: reservation of conference rooms for the plenary and parallel sessions, the ceremonies, the workshops and poster exhibition already made in the beginning of 2020 had to be cancelled, and with a heavy heart, we had to understand that there would not be any social events and excursions, which normally are essential and popular parts of any scientific meeting.

Fortunately, the organisation in Leuven enjoyed the professional support by KU Leuven Conference Office. We decided to choose a digital platform that gave the maximum look and feel of a physical conference, and, at the same time, took advantage of the opportunities provided by a virtual event with interactive online sessions, professional video streams and pre-recorded individual presentations. We tried to simulate a live event as much as possible, considering the different time zones in the countries across the five continents. This way, we could offer the presenters of posters the possibility of short enlightenment talks as well, which brought poster papers closer to oral presentations.

Finally, we could feature three keynote and four invited speakers. Their talks were delivered in live sessions. Furthermore, out of the accepted oral presentations, six premium talks were selected for live presentation. The main criterion for selection was the topic, of course besides the quality. All other presentations have been uploaded for access via the platform and could be viewed during and even after the conference. The complete conference was recorded, and the livestreams were available for registered participants until 15 October 2021.

In total, 411 participants from more than 40 countries of five continents registered for the conference. Out of more than 300 peer-reviewed submissions, we accepted 230 papers (155 full and Research-in-Progress papers and 75 posters). We followed the tradition of the previous conferences to edit a special conference issue in the journal Scientometrics. For the present one, we invited authors of full and research-in-progress papers presented at the conference to submit extended versions of their accepted conference manuscripts, now without formal page limitation. After proper reviewing of the new submissions, we were able to select 48 original research papers, which are part of this dedicated conference issue. These papers represent the various conference topics but also the geographic variety of conference participation. Besides traditional topics, like indicator research, publication and citation analysis, mapping of science and network analysis, the collection presents a broad spectrum of topics comprising the application of advanced computer science techniques and artificial intelligence to bibliometrics, quantitative studies of the effects of globalisation, mobility and collaboration, interdisciplinarity, patent analysis and technology-related research, bibliometrics in the social sciences and humanities, gender related studies in the social context of science, bibliometrics studies on Open Science, new venues of scholarly and scientific communications, altmetrics and new metrics, societal impact. Because of the overlap and interrelation of the research topics, we present the selected contributions in alphabetic order of first authors.

The following event of this conference series will be organised in the coming year. The 19th International Conference of the International Society for Scientometrics and Informetrics will be held in Bloomington, Indiana, USA, on 2–5 July 2023. Due to the ongoing constraints imposed by the COVID-19 pandemic situation, the conference is currently planned as a hybrid event. Detailed information on organisation and participation can be found on the conference website at https://cns-iu.github.io/workshops/2023-07-02_issi/.