The enzymes involved in cheese ripening and the factors affecting their activity in cheese is reviewed. The review begins by outlining the various enzymes that contribute to cheese ripening including those originating from milk, coagulant, starter and nonstarter Lactic Acid Bacteria, and those added as exogenous preparations to accelerate flavour development. Factors influencing the retention, release and residual activity of these enzymes in cheese are discussed along with an outline of innovative methods to enhance the retention and release of exogenous enzymes. (c) 2005 Elsevier Ltd. All rights reserved.