Diverse models currently exist in the field of Software Engineering which help organizations to apply recommended practices in order to support ther multiple needs in the areas of software development, maintenance and operation, security, IT government, etc. Examples of such models are CMMI, ISO 9001, ISO 12207, ISO 27001, COBIT, ITIL. Nevertheless, many differences exist between these models, since each model defines its own structure, terminology, definitions and quality systems, amongst other aspects. This issue increases the complexity when an organization is required to apply two or more models in order to satisfy its needs. Organizations must, therefore, define the most appropriate means of choosing and implementing multi-models, and harmonization may be one solution. This paper presents a systematic literature review with the aim of analyzing the state of the art with regard to inititatives concerning the harmonization of multiple reference models. As a result, it has been concluded that there is currently a lack of guidelines with which to help organizations to implement the harmonization of multiple models, and of a unified terminology with which to homogenize the diversity of the structure of the different models and the harmonization techniques which can be applied. In order to address these issues, a framework to support the harmonization of multiple models is outlined