In this thesis, we present new protocols that provide reliable ordered multicasts to multiple overlapping process groups in the presence of failures. Our protocols provide two kinds of message delivery ordering - causal ordering and total ordering. Message delivery is also ordered with respect to the observation of group membership changes, a property known as virtual synchrony. Initially we examine solutions for the case of a single process group, and subsequently extend our solutions to encompass multiple overlapping process groups. In comparison with previous protocols for these problems, our protocols are cheaper and scale up better. An initial implementation of our protocols as part of the ISIS toolkit has produced encouraging performance results.