Silica‐based organic‐inorganic hybrid nanomaterials represent a versatile and powerful tool for bioimaging applications. Several features make silica very attractive: it is optically transparent, water dispersible, biologically inert, nontoxic and the strategies for the modification of its surface are well‐established and versatile. The coupling of these features with excellent fluorescence properties of organic and organometallic fluorophores allow the obtainment of nanosystems characterized by controllable and tunable properties. Starting from the general definition of hybrid nanomaterials, this chapter introduces several aspects related to the design, preparation, characterization and application of silica‐based organic‐inorganic hybrid nanomaterials for optical imaging. Different silica‐based architectures are discussed: (i) non‐porous fluorescent silica nanoparticles, with particular attention to the fine control of the fluorescence properties of the hybrid materials; (ii) mesoporous silica nanoparticles and the different strategies which can be followed in order to finely tune the properties of the nanosystems and to create multimodal nanoparticles; (iii) fluorescent organosilicas, prepared from 100% or less organic‐bridged alkoxysilane precursors, which are interesting organic‐inorganic hybrid materials bearing a wide variety of different functionalities, depending on the nature of the organic moieties of the framework; (iv) zeolites, in particular the recent advances in the preparation and characterization of nanosized zeolite crystals are reviewed, along with a panel of successful examples of application.