Abstract: A presence aggregation system provides a presence aggregation server that allows for the publication of presence state of a publisher from the publisher's multiple endpoints. A presence state includes an availability value and an activity. An activity may include an activity token and/or a custom string. When any one of the publisher's endpoints makes a presence state publication on the presence aggregation server, the presence aggregation server generates an aggregated state of the publisher (i.e., the availability of the publisher aggregated across all of the publisher's endpoints) and publishes the generated aggregated state to each of the publisher's endpoints. The presence aggregation server may also provide the publisher's aggregated state to the subscribers of the publisher's aggregated state information. (end of abstract)