A variety of organizations around the world use complex information systems (e.g., enterprise resource planning and supply chain management systems). However, poor usability caused by system complexity continues to frustrate users and damage the reputation of these systems. In this study, we address usability issues with complex information systems from the human-computer collaboration perspective by modeling user-system interaction as a joint activity between the system and its users. We propose a conceptual model for user-system collaboration, elaborate on the components in the model and the relationships between the components, derive the required capabilities for collaborative information systems, and establish conceptual relationships between system collaborative behaviors and usability. We use empirical evidence gathered from a qualitative field study on ERP systems to illustrate the model and the possible impact of system collaborativeness (i.e., the presence or absence of collaborative capabilities) on usability. We do so to provide a strong conceptual foundation for modeling user-system collaboration and to encourage designers to employ the collaboration metaphor during system design and, thus, help them develop future complex information systems with better usability.