Cell surface proteins are proteins that are embedded in or span the layer of cell membranes of more complex organisms. These proteins are integral to the way in which a cell interacts with the environment around it, including other cells. Some of these proteins, especially ones that are exposed to the external side of the membrane, are called glycoproteins because they have carbohydrates attached to their outer surfaces.

Jagged1 (JAG1) is one of five cell surface proteins (ligands) that interact with 4 receptors in the mammalian Notch signaling pathway.