Ballot Measure 37, a property rights initiative passed by Oregon voters in November 2004, requires Oregon's state and local governments to compensate landowners for any reduction in the value of real property due to land use regulation or else to waive the offending regulations. This Note addresses the scope of an important exception to Measure 37: the law does not apply "to the extent that the land use regulation is required to comply with federal law." The ambit of this exception is questionable because many federal environmental laws, some with significant land use implications, involve a partnership approach called cooperative federalism where federal agencies set broad goals and states are responsible for on-the-ground implementation. This Note surveys Measure 37's federal law exception in its textual, regulatory, and constitutional contexts and concludes that the most tenable interpretation is a broad one: Measure 37 does not apply to land use regulations in federally approved plans and programs that represent Oregon's efforts to comply with federal law. This interpretation is reinforced by a clarifying definition of "federal law" in Ballot Measure 49, an initiative subject to a November 2007 special election vote.