Environmental marketplace advocacy represents a form of corporate issue advocacy and a significant source of environmental communication for the U.S. public. This study tested a model of environmental marketplace advocacy, conceptually grounded in the persuasion knowledge model, with a national U.S. audience. The model predicted 78% of variance in attitudes toward the advertiser and its environmental impact. Contrary to expectations, participants’ environmental concern was positively associated with persuasion; this effect was reversed among those with a graduate degree, a background in science, or membership in an environmental organization. Important implications for both corporate and environmental advocacy are discussed.