The primer addresses the basic concepts of model-based systems engineering. It covers the model, language, behavior, process, architecture, and verification and validation. It is a call to the consideration of the foundational principles behind those concepts. It is not designed to present novel insights into MBSE so much as to provide a guided tour of the touchstones of systems design. It is a guide to the new MBSE acolyte and a reminder to the experienced practitioner. It is suitable for use by a systems engineer new to the practice of “model-based” systems engineering, an experienced systems engineer who has been introduced to “model-based” concepts in an ad hoc fashion or by any professional knowledgeable of systems thinking and practice. It is not intended as a comprehensive guide or as a practice handbook.