S-adenosylmethionine (SAM)-dependent enzymes play an important role in all kingdoms of life. SAM is used as a methyl donor for the methylation of small molecules, proteins, and ribonucleic acids by conventional methyltransferases. It is further the cofactor for radical SAM enzymes that can catalyse a multitude of complex reactions, including methylations at unactivated positions. In the wide field of epigenetics, methylations are also an important marker, an example are methylations of nucleobases that are introduced by conventional and radical SAM methyltransferases. The reactions catalysed by SAM-dependent enzymes are highly interesting for technical application, e.g. the synthesis of selectively methylated building blocks for pharmaceuticals. Often, the corresponding synthetically-chemical version of the reaction uses highly toxic and cancerogenic compounds and is rather unselective. In the AppSAM project, we developed strategies to integrate SAM-dependent enzymes in multi-enzyme cascades to facilitate their handling and efficiency for chemical synthesis. These systems are also useful for the mechanistic-functional investigation of SAM-dependent enzymes, e.g. from epigenetic pathways or natural product biosynthesis, using modified (co-)substrates that can be produced in situ. In addition to in vitro multienzyme systems, different in vivo systems have been explored with a range of enzyme/ substrate combinations.