Layered double hydroxides (LDHs) are clay-type materials with extraordinary properties, whose structure is composed of stacked inorganic metal oxide layers built by connected sheets. The crystal structure of layered double hydroxides is based on positive charged brucite-like mainlayers and balanced by reversible exchangeable interlayer anions, additional cations and water molecules. Due to their negligible toxicity and buffering properties, LDHs are commercially employed as antacids and they are increasingly studied as vehicles in drug and gene delivery systems. This book discusses the synthesis, characterization and applications of layered double hydroxides.