Group communication, providing virtual synchrony semantics, is a powerful paradigm for building distributed applications. For applications that require a large number of groups, significant performance gains can be attained if these groups share the resources required to provide virtual synchrony. A service that maps multiple user groups onto a small number of instances of a virtually synchronous implementation is called a Light-Weight Group Service.This paper describes the design of a lightweight group service able to operate in partitionable networks. Partitions pose challenges to the design of this service, in particular because inconsistent mapping decisions can be made when the system is partitioned. The paper focuses on the design of reconciliation mechanisms needed when a partition is healed.