LIMBS is an open source brokerage system developed in the framework of the CALIBRATE project. LIMBS relies on open standards and open contents to promote exchanges of learning resources within a federation of e-learning systems. Contrary to the CELEBRATE brokerage system, from which it derives, LIMBS?s role is limited to carrying and routing messages exchanged by the federation members rather than to enforcing semantic interoperability. With LIMBS, semantic interoperabili-ty becomes the responsibility of the federation members that rely on "clients" to communicate with the brokerage system and to support the negotiation of common query languages and metadata formats. LIMBS itself adopts a serviceoriented architecture so that each service (e.g., resource discovery, digital rights management) can be used separately and combined with any (group) of the others.