This paper presents our research on awareness support in Instant Messaging (IM). The paper starts with a brief overview of an empirical study of IM, using an online survey and face-to-face interviews to identify user needs for awareness support. The study identified a need for supporting four aspects of awareness—awareness of multiple concurrent conversations, conversational awareness, presence awareness of a group conversation, and visibility of moment-to-moment listeners and viewers. Based on the empirical study and existing research on awareness, we have developed the F@ (read as “fat”) framework of awareness. F@ comprises of an abstract level and a concrete level. The former level includes an in-depth description of various awareness aspects in IM, whilst the latter level utilises temporal logic to formalise fundamental time-related awareness aspects. F@ helps developers gain a better understanding of awareness and thereby design usable mechanisms to support awareness. Applying F@, we have designed several mechanisms to support various aspect of awareness in IM.