From Silicon Valley to BIBLIOPOLIS. Micro-cluster of Poznań libraries collecting legal and economic literature. The aim of the following presentation is to show the experience and initiatives of the co-operating informal working group composed of the representatives of different libraries of the town. The novelty included in the venture is that it concerns co-operation and joint activities of libraries of different types despite formal constraints hampering this co-operation within the broadly understood scope the target subject, i.e.law and economics. In practice, the co-operation involves specialization in relevant collection holding areas through consultations as to the acquisition of sources (both traditional and electronic), information of the collections and joint (and thus more economic) use of own resources as well as through popularization of modern economic knowledge within the library community. This activity is presented in the light of one of the most modern and dynamically developing theories of regional co-operation known as clusters.