Functional hybrids are nanocomposite materials lying at the interface of organic and inorganic realms, whose high versatility offers a wide range of possibilities to elaborate tailor-made materials in terms of chemical and physical properties. Because they present several advantages for designing materials for optical applications (versatile and relatively facile chemistry, easy shaping and patterning, materials having good mechanical integrity and excellent optical quality), numerous silica or/and siloxane based hybrid organic-inorganic materials have been developed in the past few years. The most striking examples of functional hybrids exhibiting emission properties (solid-state dye lasers, rare-earth doped hybrids, electroluminescent devices), absorption properties (photochromic), nonlinear optical (NLO) properties (second-order NLO properties, photochemical hole burning (PHB), photorefractivity), and sensing are summarized in this review.