Some proteins are now classified as being knotted. However, proteins have free ends and knotting, mathematically, is only defined for closed curves. Defining knotting in open chains is tricky and ambiguous. We will show one definition of open knotting and search for knotted arcs within knotted open, closed chains, and proteins. This is joint work with Ken Millett, Andrzej Stasiak, and Joanna Sulkowska.