Fibroblasts, are mesenchymal cells from the embryonic mesoderm. Fibroblasts secrete a non-rigid extracellular matrix that is both rich in type I and/or type III collagen. They are responsible of the synthesis of extracellular matrix in connective tissues and play a central role in wound healing. They are useful tools for a wide range of cellular and molecular studies, as they are one of the easiest types of cells to grow in culture. In addition, their durability makes them amenable to a variety of manipulations ranging from gene transfection to microinjection. Human Small Intestine Fibroblasts are an excellent tools to study the small intestine physiology and also the mechanisms of carcinogenesis.