Abstract— This paper presents a new development of selforganizing maps (SOM), realized by combining them with the idea of a modular network. This we called a modular network SOM (mnSOM) in which each reference vector unit of a conventional SOM is replaced by a functional module. Since users can choose the functional module from any trainable architecture such as neural networks, the mnSOM is very flexible as well as having a high data processing ability. In this paper, we first introduce the basic idea and then describe its theory. Finally we introduce some applications of mnSOMs.