RAND has examined the procedures used to conduct life cycle analyses and estimating techniques that are often the basis for life cycle cost estimates. This study was directed at identifying shortcomings that limit the usefulness of results to decisionmakers faced with investment decisions. The procedures followed in a number of recent analyses on Air Force programs were examined as case studies. A number of procedural problems were identified that could make a cost estimate an unreliable basis for an investment decision. A review of a number of well-known models often used in life cycle analysis led to the conclusion that standard or generalized models are largely insensitive to many potentially important, real-world cost drivers. The models can be improved; but, particularly in the immediate future, sound cost estimates must rely on improved analytical procedures.