Layered double hydroxides (LDH), also referred as hydrotalcite like compounds (HTlc), constitute a large group of natural and synthetic minerals whose physico-chemical properties have strong analogies with clay minerals and more particularly with cationic clay minerals. In the first part, LDH are described in terms of natural and synthetic chemical compositions. The various methods of preparation and the tailoring of textural properties are reported. Recent developments in novel synthesis (microwave, ultrasound) and in preparation of LDH with specific morphology were introduced. A full description of the structure of these layered compounds is made in relation with the versatility of their chemical composition and their unique anion exchange and intercalation properties by different instrumental techniques (solid-state NMR, X-ray diffraction and absorption, FTIR and Raman, etc.). The second part gives an overview of the fundamental properties such as chemical stability, thermal behaviour and colloidal properties.