Object-oriented modelling is used in a growing number of commercial software development projects. However, the plethora of approaches and corresponding CASE tools still prevents corporate users to migrate to object-oriented software development methods. Against this background the recent efforts of the Object Management Group (OMG) to standardize objectoriented modelling languages seem to promise substantial benefits: Not only will a standard allow to easily port a model from one CASE tool to another, it will also protect investment in training. In addition, it is a prerequisite for standardized business object models which - in the long run - may substantially improve the economics of developing and maintaining corporate information systems. Nevertheless there are objections against a standardization at present time: It is questionable, whether the state of the art in object-oriented modelling is mature enough to allow for standardization. Furthermore standardization holds the risk to discourage further innovations. In order to analyze the state of the art, this report will first give an overview of previous approaches to object-oriented modelling. To get an idea of the present state of the art, the essential characteristics of the modelling languages currently under review at the OMG are briefly characterized - together with an additional approach that recently has gained remarkable attention. This will lead to a number of research challenges still to overcome. Finally the report offers a subtly differentiated answer to the question whether or not it is time for standardizing object-oriented modelling languages.