In the course of designing, writing and implementing CALL-supported material, it has become evident to me that a systematic investigation into the factors that shape the Blended Learning (BL) experience in the context of language learning and teaching is missing and urgently needed. The core question when designing a BL environment is: Which combination of modes provides the optimal basis for language learning and teaching given the particular conditions at hand? In order to tackle this question, course designers need a framework of parameters that help them decide on the individual, context-related implementation of BL. It is the purpose of this paper to put forward a definition of BL and a framework of parameters for designing a BL environment. In order to achieve a better understanding of the factors that shape the practice and the experience of BL, the main parameters which form a BL environment will be listed and specified. These parameters evolved from the experience of designing Jobline LMU (www.jobline.lmu.de) and will hopefully prove to be helpful for the process of designing other BL environments. If applied successfully, the idea of BL could serve as a bridge between the broader community of language teachers and learners and CALL experts and practitioners. BL offers the potential of broadening the scope and influence of CALL and of (re-)establishing it as an innovative component of general language teaching.