This mini-workshop is devoted to collective effects and electron cloud studies in circular accelerators. The investigation and comprehension of collective effects is fundamental for the success of accelerators. In particular the electron cloud instability poses severe limitations to the performances of colliders or damping rings for linear colliders. These topics were deeply studied with great competence and passion by our colleague Theo Demma, who passed away a year ago. Theo was a special person and a friend for many of us and we dedicate this afternoon to his memory.