Connective tissue is characteristic of all organisms of the animal kingdom; however, the composition can be very different, since specialized connective tissue cells are responsible for the production of different intercellular components. The latter combine to form the Extracellular Matrix (ECM), for which fibre components from chain molecules are fundamental, in particular from the collagen group. Such chain molecules, but also other swellable components of the matrix, form the starting point for the various connective tissue stains.