AbstractDevelopment of complex systems is a collaborative effort spanning disciplines, teams, processes, software tools, and modeling formalisms. Increasing system complexity, reduction in available resources, globalized and competitive supply chains, and volatile market forces necessitate that a unified model‐based systems engineering environment replace ad‐hoc, document‐centric and point‐to‐point environments in organizations developing complex systems.To address this challenge, we envision SLIM—a collaborative, model‐based systems engineering workspace for realizing next‐generation complex systems. SLIM uses SysML to represent the front‐end conceptual abstraction of a system that can “co‐evolve” with the underlying fine‐grained connections to models in discipline‐specific tools and standards. With SLIM, system engineers can drive automated requirements verification, system simulations, trade studies and optimization, risk analyses, design reviews, system verification and validation, and other key systems engineering tasks from the earliest stages of development directly from the SysML‐based system model. SLIM provides analysis tools that are independent of any systems engineering methodology, and integration tools that connect SysML with a wide variety of COTS and in‐house design and simulation tools.We are presenting SLIM and its applications in two papers. In Part 1 (this paper), we present the motivation and challenges that led to SLIM. We describe the conceptual architecture (section 1) and use cases (section 2) of SLIM followed by tools available for production and evaluation usage (section 3). In Part 2 paper—SLIM Applications—we present the applications of SLIM tools to a variety of domains, both in traditional as well as non‐traditional domains of systems engineering. Representative examples from space, energy, infrastructure, manufacturing and supply chain, military operations, and bank systems are presented.