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This paper reviews ongoing progress in exploring the mechanistic origins of photoinduced structural modification in chalcogenide glasses (ChGs). These findings, reported by groups at the University of Central Florida, Clemson University, and throughout other research programs within the United States and abroad, have examined the relationship between the network modification and other photoresponse of IR glasses upon exposure to near-infrared (NIR) femtosecond laser exposure. Contained is a review on the principles of femtosecond laser writing in glass, the photoinduced phenomena, and a summary of the main models predicting photoinduced material response. We compare the photoresponse of As- and Ge-based films, taken as example, following NIR femtosecond laser irradiation that results in near-surface photoexpansion and an increase or decrease of the refractive index, respectively. This difference in photoresponse has been related to the "layered" network of the As-based glass that leads to the breaking and formation of bonds during laser exposure as compared to the 3-D network of Ge-based glass that leads only to a modification of the bond arrangements. Last, an explanation of the need to control the photoresponse of ChGs by aging, changing the glass thermal history, adding modifiers, or replacing the anions forming the network is discussed.