Most of the published actuarial literature in the U.K. on immunization has been applied to the valuation of a life office. The authors have shown how the immunization techniques first introduced by Redington (3) in 1952 can be used to match the liability outgo of the office, to a greater or lesser extent.

The purpose of this paper is to introduce the student to the underlying concept of immunization and to show how it can be utilized to produce a guaranteed rate of return with a high degree of probability, irrespective of the future course of interest rate levels.

The term to maturity and duration (mean term) of a bond are discussed in §2. The maturity is only of limited help in characterizing a specific bond. The duration—a measure of the average time until the bond payments are received—is an easily determined figure which is more informative about a bond than maturity. The price sensitivity of a bond (i.e. volatility) is linearly related to the duration.