The ability to detect a broad range of chemical species in the atmosphere, geosphere, and hydrosphere, over a wide range of ambient levels and conditions, is a key enabling technology both for environmental monitoring and for sensing the presence of hazardous materials such as explosives or chemical agents. In this paper we describe several recent developments in the area of high-sensitivity chemical monitoring, including Cavity RingDown Spectroscopy (CRDS) and Raman spectroscopy. Significant improvements in the sensitivity of both ultraviolet and infrared CRDS have been made in our laboratory during the past year. Infrared CRDS, employing tunable infrared optical parametric oscillators, multilayer dielectric high-reflectivity mirrors, and membrane preconcentrator technology, may have the potential for detecting vapors from concealed explosives as well as a wide variety of volatile organic compounds present at parts-per-billion levels or below. Sensitivity enhancement techniques for Raman spectroscopy, such as Surface-Enhanced Raman Spectroscopy, may achieve similar sensitivities for samples in ultra-dilute solutions. We also address the relationship of novel monitoring techniques, such as these high-sensitivity detection methods, to current and future regulatory issues.