The 8th International Polychaete Conference (IPC 8) was held in Madrid, Spain, from July 4–9, 2004, bringing together 180 scientists from 26 countries. Hosted at the Universidad Autónoma de Madrid, the conference offered a lively mix of oral presentations, posters, plenary lectures, and commemorative talks honoring the legacy of past polychaetologists. In total, 47 talks and 127 posters were presented, reflecting the broad scope of research in systematics, ecology, morphology, and more.The week also included a one-week course on cladistics and polychaetes, taught by Arne Nygren, Fredrik Pleijel, and Greg Rouse, continuing the IPC tradition of combining scientific exchange with training for early-career researchers. A mid-conference excursion to Segovia and El Escorial gave participants the chance to explore Spain’s cultural heritage. The conference proceedings — including 37 peer-reviewed papers and several memorials — were published as a supplement in Scientia Marina.