Today there is an emerging tendency – from aesthetical and economical concerns – to create/refurbish venues for a wide variety of performance types, each demanding a specific acoustic. For these multi-purpose halls, electro-acoustic enhancement systems represent the most promising approach, allowing high quality results with the greatest flexibility. This paper reviews the principles of the main categories of reverberation enhancement systems that have been designed and commercialized in recent decades. General and specific constraints of these categories of systems are presented with a set of evaluation criteria and guidelines for selecting a system for use in a given hall and performance context.