Secretary of the Interior Ryan Zinke's review of 27 national monuments has focused new attention on the Antiquities Act of 1906. Two recent proclamations by President Trump reducing existing Utah monuments, and the potential for further actions by the president and Congress, may substantially affect the future shape and effect of this important law. On December 7, 2017, ELI held a seminar to explore presidential and congressional authority in declaring and modifying national monuments. Panelists discussed the Act's legal history, the importance of existing national monuments, the role of Congress in managing these lands, and what might be expected from pending court challenges. Here, we present a transcript of the discussion, which has been edited for style, clarity, and space considerations.