Ring maps are used in Macaulay to change or specialize the value of various variables, to change the monomial order used, to add new variables, etc. Ring maps are represented in Macaulay as matrices with one row. One creates a general ring map either with rmap, or by using the various matrix operations. For special types of ring maps, i.e. ring inclusions or projections, one can use imap to define such a ring map, or one can implicitly use such a ring map with the command fetch. The most important command is ev, which performs the evaluation of a matrix with respect to a ring map.