Traditionally, research in electronic negotiations support has concentrated on monolithic negotiations, i.e. negotiations in which parties are unitary decision entities. In this paper, a model for non-monolithic electronic negotiations is introduced. This model, named the contract-group-message model, integrates a multiversion contract model, and support for group dynamics and message exchange. Design of support systems for non-monolithic electronic negotiations based on the contract-group-message model is also presented in this paper.