This paper describes the progress of the I/ITSEC conferences and the corresponding growth of Modeling & Simulation (M&S) over the fifty years from the initial convening to this year's conference. I/ITSEC began as a Navy/Industry conference and later it was combined with the other services to become a truly “interserviceâ€� event. The very first “industryâ€� conference can be described as the “Big Bangâ€� of simulation and training. It was held in 1966 at the Orlando Air Force Base, Florida and orchestrated by the Naval Training Device Center (NTDC). The conference was the beginning of an expanding universe of M&S and reflective growth of I/ITSEC. From its humble beginning with 49 industry attendees, the conference grew over the years to a projected 14,000 people this year, coming from all points of the globe. The venue for the original conference was an old World War II building, with a failing air conditioning system and an overhead projector-a sharp contrast to the spacious Orange County Convention Center, with the impressive simulation technology exhibited. The stage is set leading to the “Big Bangâ€� by describing the simulation environment in the early 1960's with the Navy occupying the Gould (Guggenheim) Castle at Sands Point, N.Y. In 1965, NTDC moved its workforce of military and civilians to Orlando, Florida. Critical points in the growth of the simulation industry and I/ITSEC are addressed. Throughout its history, the simulation industry has been influenced by visionaries, innovators and managers making decisions and policies that have set and/or altered its course, growth and effectiveness. Management decisions were made outside of the military that caused major shifts in the organizations involved and other decisions were made within the system the events and decisions having the most impact will be identified as well as the author's observations and “lessons learnedâ€� are summarized.