When metamodels evolve, model conformity may be broken. This forces the owners of the models (modelers) to intervene because it is impossible to automatically discover what to change in order to regain conformity. This paper presents ASIMOV, a platform for model and metamodel co-evolution based on two hypothesis: i) a metamodeler knows the rationale behind metamodel changes, and is capable of providing guidelines for model coevolution; ii) the modeler is the only one in grade of making final decisions about his models. ASIMOV provides two languages for metamodelers: ASIMOV Evolution, to specify changes in the metamodels; and ASIMOV Assistance, to propose corresponding changes in the models. Also, ASIMOV Engine solves automatically the changes in models that can be automatically solved and assists modelers in coevolving their models to regain conformity. Moreover, modelers can adapt the proposed changes to suit their particular needs, introducing additional information when it is required. ASIMOV is here illustrated in the context of Enterprise Architecture projects.