Functionalization of dielectric materials such as crystals, glasses (silica-related or polymers), and liquid polymerizable resins by femtosecond (100-500 fs) irradiation is summarized. The modification was carried out by employing tight focusing optics with numerical aperture typically NA > 0.6. This allows to produce 3D optical memory and photonic crystals (PhC) by implementing a principle of the focal spot scanning inside silica glass or polymerizable resin. PhCs can be also fabricated by encoding the 3D hologram in negative polymer photoresist. Optically modified regions of dielectric were found to respond sensitively to wet etching. The contrast in the etching rate is over 50, which makes it possible to fabricate 3D channels for microfluidics inside dielectrics.