My early research was in network reliability and basic graph theory. Since 1985 it has focused on hamilton cycles and long cycles in graphs; in particular, the relationship between the toughness of a graph and its cycle structure. I have also studied the computational complexity of recognizing toughness in various classes of graphs. In the last few years my work has focused on matchings in graphs and the properties of Tutte sets, as well as the interplay between the connectivity of a graph and its cycle structure. I am currently working on degree sequences, and finding strongest monotone bounds for various graph parameters.