Interest rates are, with probability one, not constant over the course of life insurance risks. As remarked by Hickman (1985), “Interest rate variation and resulting risk is a fact of business life.” Fortunately, previously developed concepts based on the present value of loss variables extend immediately to the case where the interest environment, although non-constant, is known in advance. We can quantify the impact of uncertainty in the interest environment by introducing concepts of diversifiability for a portfolio of risks. Modeling uncertainty in the interest environment requires complex tools – this module introduces simulation techniques as one such useful tool.