This document describes the implementation of a group telephony feature commonly known as Bridged Line Appearance (BLA), Multiple Line Appearance (MLA), or Shared Call/Line Appearance (SCA). When implemented using the Session Initiation Protocol (SIP), it is referred to as Multiple Appearances. This feature is commonly offered in the IP Centrex services and IP-PBX offerings and is likely to be implemented on SIP IP telephones and SIP feature servers used in a business environment. This specification defines a new SIP dialog event package tag "appearance" and a method for a group of SIP user agents to coordinate the identification of appearances between them using SIP dialog package subscriptions.