This book contains the papers that were delivered during the 16th liturgical colloquium of the Liturgical Institute of Leuven in October 2003. The colloquium dealt with the notion of 'active participation' on the occasion of the 100th anniversary of Tra le sollecitudini and the 40th anniversary of Sacrosanctum Concilium. Paul De Clerck (Paris) presents a historical retrospect. Paul Post (Tilburg) gives a panorama of current ritual-liturgical inculturation. Thomas Pott (Rome) reflects on the spiritual dimension of liturgical participation. Liliane Voye (Louvain) deals with participation from a sociological point of view. Andre Haquin (Louvain) and Andre Goossens (Antwerp) discuss the challenges of a liturgical assembly.