Here we provide an overview to a set of papers that analyze various facets of the shift to cash balance and other hybrid pension forms that has become controversial and widely discussed phenomenon in the evolution of private, employer-sponsored pensions in the United States. These new plans take on the characteristics of defined contribution plans from the perspective of workers but continue to be funded and operated as defined benefit plans from the perspective of plan sponsors. The shift to this new style of plans began in the mid 1980s but then took off and accelerated toward the end of the 1990s. This paper describes the context in which this shift in plan types being offered by employers took place because it helps to explain various features of these plans addressed in the remaining papers and the underlying reasons that employers have adopted the new plans. The latter part of this paper provides a very brief summary of the conclusions drawn from the remaining papers in the set.