Microfacies types document differences in the kind of and significance of sedimentological (affecting sediment) and biological (affecting organisms) environmental factors. Although during the genesis of facies units there is an interplay of several factors, some environmental factors — especially in marine areas — seem to be of major importance. Based on the ideas expressed by J. Walther (1893) and H. Schmidt (1956), and in keeping with the special conditions necessary for limestone formation, the following controls are active for: 1. Sedimentation: a) Organic activity b) Water movement or energy levels (energy produced by waves or currents in the boundary zone between water and the sedimentary substrate) c) Suspended terrigenous influx (influx from continents, sedimentation of non-carbonate particles and of carbonate extraclasts; see Sects. 4.1.3.8 and 4.1.4) d) Processes of cementation, particularly during early diagenesis (see Sect. 3), and during various stages of dissolution 2. Organisms (non-biological factors) a) Light and water depth b) Water energy and oxygen supply c) Salinity of the water d) Water temperature e) Composition and consistency of the substrate