We present an ultrahigh vacuum study of the carbon monoxide–silver system using Raman scattering.Silverfilmsdeposited in UHV on a room‐temperature substrate cooled close to 78 K and exposed to saturation doses of CO show Raman lines at 1995 and 2070 cm−1. These disappear upon warming to room temperture. Films freshly deposited on a cooled substrate show a line at 2010 cm−1 which appears at 10 L and grows in intensity through 105 L. A second line, thought to be due to residual CO, is visible on the fresh film at 2124 cm−1 and shows only minor changes with CO exposure. Further study of surfaces prepared in this manner shows at least 16 lines in the region 40–2600 cm−1 after exposure to 105 L of CO. Analysis of the data shows the utility of Raman scattering as a surface probe.