The U.S. House of Representatives passed House Resolution 487 in 2007 recognizing modeling and simulation (M&S) as a national critical technology. The niche technology of M&S applies mathematics and computer science to disciplines across academia, industry, and the government. The use and development of M&S depends on expertise in science, technology, engineering, and mathematics (STEM) as well as the specific disciplines to which the technology is applied. These disciplines include manufacturing, healthcare, medicine, instructional systems design, fluid dynamics, social science, and military science to name only a few. Uses of this technology include analysis and decision support; engineering and design; studies and experimentation; and training and education. The developed simulations might be live, virtual, or constructive; discrete event; process; agent-based; systems dynamics; another paradigm; or a combination of multiple paradigms. M&S expertise required includes services such as management and decision support on M&S use and application; support such as custom development and verification, validation, and accreditation; specialized support in the use of specific M&S simulation development; and data support and integration to name a few. This wide range of discipline domains, uses, and specialized M&S expertise makes it difficult to simply describe the education, training, and job of the M&S professional. The development of the Certified Modeling and Simulation Professional (CMSP) and multiple efforts to compile an M&S Book of Knowledge and the launching of the National Modeling and Simulation Coalition have done little to clarify this. This paper examines what it means to be a professional in the field of M&S by providing an examination of the ecosystem comprised of M&S required skillsets, the subject matter required for its support, and its applications in order to provide a tighter bound on what it means to be a professional of M&S.