The implementation of multiscale methods follows different strategies, each with their own advantages and limitations. The addition of multiscale modeling capabilities to existing programs can follow two principal strategies for coupling the methods, which can be categorized in terms of tight and loose coupling approaches. In their extreme versions, a tight coupling strategy has the methods integrated in a single monolithic program with a high degree of interdependency, whereas a loose coupling strategy avoids interdependencies as far as possible by implementing the individual methods in separate programs or by providing either part in a library.