Following a successful first leg of this Joint Symposium organised by Jagiellonian University in Kraków, Poland, the second leg was hosted by the Grotius Centre for International Legal Studies, Leiden University, The Netherlands. The overall topic of the symposium was “Exploring the Frontiers of International Law in Cyberspace”, taking aim at the challenges posed by cyberspace to traditional notions and areas of international law in light of the interconnectedness of global networks, our growing dependency on information and communication technologies and malicious behaviour by States and non-State actors. The Leiden event focused on the role and impact of cyberspace with respect to human rights and the environment. The event was held online on 25 June 2021.