Ultrashort laser pulses, i.e., pulses emitted shorter than a picosecond, can tailor material properties by introducing permanent modifications locally in three dimensions. Remarkably, under a certain exposure condition, these modifications are accompanied by self-organized patterns with nanoscale periodicity. These peculiar light-induced structural and morphological modifications raise numerous intriguing material questions, in particular, related to their formation mechanisms and characteristic features that are to date largely unanswered. In this thesis, we investigate the femtosecond laser response of selected complex glass systems. Specifically, this thesis reports laser-induced modifications and self-organization in the ultra-low expansion (ULE), tellurite, and chalcogenide glass systems based on post-mortem observations and analysis. With multiple objectives in this comparative study, we aim to outline complete modification lists for selected glass systems within the parametric window, determine laser exposure conditions to sustain/annihilate self-organization and unravel the role of key material properties on the formation of local modifications along with self-organized patterns. The final objective is to engineer smart materials and devices based on laser-induced localized transformation. This thesis reveals numerous unprecedented laser-induced modifications. Unusual physiochemical properties of the representative glass systems lead to 1) a few common modifications, such as photo-contraction, photo-darkening, valence state change, and ion migration. The amorphous nature of the modification is preserved by rearranging the glass network, while the laser-affected zone of chalcogenide glass exhibits fluence-dependent density and refractive index variations. 2) Less common modifications, such as crystallization, require either a metastable system or extreme processing conditions. Specifically, under a given condition, glass decomposition of tellurite and ULE glass generates localized nanocrystalline precipitates in the glass. 3) Self-organization, strongly dependent on laser parameters, is typical on the surface of all selected glass systems; further dependency on the electronic and thermomechanical properties of the glass can suppress their formation in the volume. Such volume nanogratings are not present in the tellurite glass, although salient features are achieved on its surface. 4) Particularly, the etching selectivity of laser-modified material opens up the possibility to fabricate monolithic substrates in chalcogenide and ULE glass, and semiconducting nanocrystals in the laser-affected area enable UV photodetection in tellurite glass. Overall, this thesis provides new insights toward a general understanding of how dielectrics behave under femtosecond laser irradiation and serves as a guideline for future in-situ experimentation.