For the integration of electronic negotiation systems within information systems, it is essential to model both using the same modelling paradigm to avoid frictions. We develop a generic model of electronic negotiations using Petri nets as a formal base focussing especially on the underlying processes. We introduce a negotiation scenario from which we derive the relevant processes, protocols and information objects, explaining the motivation for negotiations as well. Our approach is modular and allows an extension in various dimensions - however in this paper we concentrate on the idea of integrating electronic negotiations within business processes. As such, our models can be used as formal guide for integrating negotiation environments within workflow management systems and for simulating and verifying electronic negotiation scenarios.