Description: This paper, originally published in 1992 in the Transactions of Society of Actuaries Vol. 44, deals with a topic that is becoming increasingly important to actuaries in most fields of practice. “Without relying on formulas, this paper presents the important concepts underlying the theory of arbitrage-free pricing of interest-rate-contingent cash flows.” This paper, by James A. Tilley, won the 1992-93 Annual Prize, and the Halmstad Prize for 1992. The paper includes written discussion and the author’s review of the discussions.