No longer only a tool of public interest groups, an ever expanding group of plaintiffs – including commercial plaintiffs – are using the citizen suit provision of the Resource Conservation and Recovery Act (“RCRA”), 42 U.S.C. § 6972, to address alleged regulatory violations, seek cleanup of wastes alleged to be causing an imminent and substantial endangerment, and pursue fee awards. In addition, RCRA citizen suits have moved beyond traditional allegations of subsurface wastes migrating to soil and groundwater, and may include claims such as vapor intrusion. In light of this diversified landscape of plaintiffs and media, defendants should consider the following key questions when sued under RCRA’s citizen suit provisions.