Knots in Washington XL. March 10, 2015, 10:00–11:00am Title. In memory of Sergei Duzhin (1956–2015) Abstract. I will recall life and work of my lifelong friend Sergei Duzhin who suddenly passed away on February 1, 2015. The main topic of my collaboration with Sergei Duzhin was Vassiliev knot invariants. Thus the mathematical part of my talk will concentrate on the theory of these invariants. I will first give definitions, survey the theory, and then explain our results and their further developments. I will then briefly talk about Duzhin’s life and some other of his results.