After the successful edition of 2018, we are glad to announce the 2nd Complexity72h on 17-21 June 2019 at IMT Lucca. The workshop Complexity72h is an interdisciplinary event whose aim is to bring together young researchers from different fields of complex systems. Inspired by the 72h Hours of Science, participants will form working groups aimed at carrying out a project in a three-day time, i.e. 72 hours. Each group's goal is to upload on the arXiv a report of their work by the end of the event. A team of tutors will propose the projects, and assist and guide each group in developing their project. Alongside teamwork, participants will attend lectures from scientists coming from different fields of complex systems, and applied workshops. The workshop is organized and will be hosted by the IMT School for Advanced Studies Lucca.