This paper aims to propose an extension of SOMs called an “SOM of SOMs,” or SOM2, in which the mapped objects are self-organizing maps themselves. In SOM2, each nodal unit of the conventional SOM is replaced by a function module of SOM. Therefore, SOM2 can be regarded as a variation of a modular network SOM (mnSOM). Since each child SOM module in SOM2 is trained to represent a manifold, the parent SOM in SOM2 generates a self-organizing map representing the distribution of the group of manifolds modeled by the child SOMs. This extension of SOM is easily generalized in the case of SOMn, such that “SOM2 as SOM of SOM2s.” In this paper, the algorithm of SOM2 is introduced, and some simulation results are reported.