Broadband sum frequency generation has been used to characterize glass surfaces functionalized with siloxanes containing terminal carboxylic acid and ester functional groups. omega-Ester silanes can be used in the preparations of ester-functionalized glass surfaces, which yield acid-functionalized surfaces via hydrolysis. This general methodology can be used in environmental, biochemical, or materials science surface chemistry to generate surfaces with tunable physical and chemical properties. Definitive characterization of these carboxylatefunctionalized glass surfaces can be performed in the C-H vibrational frequency region using sum frequency generation.