The affordable and reproducible creation of nanoscale functional material layers is a key desire towards the progressing miniaturization of devices and the continuous increase of data storage densities. While top-down structuring costs are exploding, the self-assembly [1] of dedicated building blocks in functional molecular layers provides an alternative to produce structures in the few nanometer range. Several different approaches, exploit characteristic materials properties for this purpose: A) the dedicated assembly of two dimensional molecular layers on prepatterned surfaces provides the basis for structural transitions involving only some hundred molecules. These transitions can be reversibly triggered by an electric field. [2] B) The complex balance of inter-molecular interactions with adsorbate-adsorbent interactions provides the basis for tuning the assembly. Long range ordering is a crucial requirement to match self-assembled functional devices with top-down manufactured methods for addressing and operation. [3] C) Using larger molecular entities and conformational flexure [4], even larger periodicity functional arrays can be manufactured by extending site blocking mechanisms to nearest neighbour interactions. [5] D) By a hierarchical two step approach, i.e. the initial assembly of a specific host-layer and the second step assembly of molecular guests upon this host layer, a wealth of new molecular properties is achievable in extended supra-molecular layers. [6] All these new supra-molecular self-assembled systems offer a valid alternative toward the fabrication of reproducibly identical and addressable “molecular switches” which are impossible to achieve by using established lithographic methods.