Infrared thermal sensing and imaging instruments, promoted by military interests as early as World War I, had evolved into serious industrial and energy conservation tools in the US by the late 1960s. The 'energy crunch' of the 1970s focused national attention on methods for saving energy. ThermoSense I, the 'First National Conference on the Capabilities and Limitations of Thermal Infrared Sensing Technology in Energy Conservation Programs' was held in 1978, sponsored by the American Society of Photogrammetry (ASP), the US Department of Energy (DOE) and the Tennessee Valley Authority (TVA). As applications for these new and exciting photonics instruments broadened into new fields such as predictive maintenance, process control, materials testing and remote sensing, the conference broadened and expanded under the sponsorship of SPIE. In the year 2003 the ThermoSense conference is being held for the 25th time. This paper traces 25 years of evolution of the applications for infrared thermal sensors and imagers as well as the improvements, innovations and refinements to the instruments themselves. Finally, some projections are made for current and near future developments in the capabilities and markets for the technology.