Business negotiation support systems (NSS) are slowly entering the market, although they lack a clear theoretical basis as of yet. Negotiation is a complicated process with many aspects that have only partially been described with the formal rigidity needed to build support systems. Most theories about negotiation are descriptive and not prescriptive, which, among other things, prevents their use as a basis for negotiation support systems. Complicating matters is that a negotiation process consists of several distinct stages, each with its own characteristics. Furthermore, there are many types of negotiations, depending on the domain. This suggests that we should not strive for one general negotiation support system, but for a set of domain-specific tools. To ground the development and application of these tools in different scenarios, we propose an integrated theoretical framework. After presenting an overview of existing negotiation support approaches, we construct a business negotiation support metamodel for NSS analysis. The metamodel is illustrated by analyzing the MeMo project, which concerns contract negotiations in small and medium enterprises in the European construction industry. The MeMo system is one of the first business NSS with an explicit international orientation.