This paper discusses the implementation of the fourth building block of the Roadmap--the public reinsurance provided to insurers who cover small employer groups and individuals in Massachusetts. Government funded reinsurance would repay insurers for 75% of an insured's allowable costs above $35,000 per year for enrollees in the nongroup market and in firms with fewer than 100 workers. The reinsurance would apply to all coverage sold, whether through the pool or outside. The paper describes the proposed public reinsurance, compares and contrasts it with other forms of reinsurance, and details the key steps to be taken in practical implementation. (Roadmap to Coverage, October 7, 2005)