CO: Twenty-Five Years of Millimeter-Wave Spectroscopy : Springer : 9780792342830 : 0792342836 : 31 Dec 1996 : Interstellar carbon monoxide (CO) was first detected in 1970 by R. W. Wilson, K. B. Jefferts, and A. A. Penzias through observations of its lowest rotational transition at 2.6 mm wavelength. This discovery opened the door to a profound new understanding of several diverse yet related fields, including the phases of the interstellar medium, the initial and final phases of stellar evolution, the chemistry of dense and diffuse interstellar matter and of the solar system, the structure of the Milky Way galaxy, and the content and structure of other galaxies. The twenty-fifth anniversary of the detection of CO was an opportunity for researchers from all branches of millimeter-wave astronomy to gather and review progress and future directions. These Proceedings discuss the state of the field and consider important unanswered questions.