Instant messaging allows users to exchange presence and availability information, and to have spontaneous online conversations. We report on a study of account sharing in IM, and present distinct types of sharing as well as practices of sharing. Author Keywords Computer-Supported Cooperative Work; ComputerMediated Communication; Instant Messaging; Sharing. ACM Classification Keywords H.5.2 [Information Interfaces and Presentation]: User Interfaces -- Graphical User Interfaces, User-Centred Design; H.5.3 [Information Interfaces and Presentation]: Group and Organisation Interfaces -Computer-Supported Cooperative Work.