CROSSING CHANGES

This is an expository survey article about the role that the simple op eration of changing a crossing has played in knot theory. Topics inclu de: the connections between unknotting number, tunnel number, and cros sing number; connections with Dehn surgery and sutured maniford theory ; nullifying crossings and the Conway skein trees; generalized crossin g changes; crossing changes and strongly invertible knots; and connect ions with 4-manifold topology. (C) 1998 Elsevier Science Ltd. All righ ts reserved.