This research study is the third in a series of surveys exploring the incidence of simultaneous media usage among a national sample of US consumers. The research is based on 12,322 respondents who were sampled via an online network. The findings show that simultaneous media usage, ie multiple exposures to various media forms at a single point in time for the same media consumer, occurs in and among a substantial portion of the US media population. The existence of simultaneous media exposures, created by multi-tasking consumers, is a fact in today's media marketplace. The existence of simultaneous media exposures undermines most current media measurement systems as they are defined as isolated environments. Thus, the challenge of this paper is for media management to rethink how media evaluations should be rethought for the 21st century. Copyright © 2004 Henry Stewart Publications Ltd.