Background: Publication of the 2015 American Thyroid Association (ATA) management guidelines for adult patients with thyroid nodules and differentiated thyroid cancer was met with disagreement by the extended nuclear medicine community with regard to some of the recommendations related to the diagnostic and therapeutic use of radioiodine ( 131 I). Because of these concerns, the European Association of Nuclear Medicine and the Society of Nuclear Medicine and Molecular Imaging declined to endorse the ATA guidelines. As a result of these differences in opinion, patients and clinicians risk receiving conflicting advice with regard to several key thyroid cancer management issues. Summary: To address some of the differences in opinion and controversies associated with the therapeutic uses of 131 I in differentiated thyroid cancer constructively, the ATA, the European Association of Nuclear Medicine, the Society of Nuclear Medicine and Molecular Imaging, and the European Thyroid Association each sent senior leadership and subject-matter experts to a two-day interactive meeting. The goals of this first meeting were to (i) formalize the dialogue and activities between the four societies; (ii) discuss indications for 131 I adjuvant treatment; (iii) define the optimal prescribed activity of 131 I for adjuvant treatment; and (iv) clarify the definition and classification of 131 I-refractory thyroid cancer. Conclusion: By fostering an open, productive, and evidence-based discussion, the Martinique meeting restored trust, confidence, and a sense of collegiality between individuals and organizations that are committed to optimal thyroid disease management. The result of this first meeting is a set of nine principles (The Martinique Principles) that (i) describe a commitment to proactive, purposeful, and inclusive interdisciplinary cooperation; (ii) define the goals of 131 I therapy as remnant ablation, adjuvant treatment, or treatment of known disease; (iii) describe the importance of evaluating postoperative disease status and multiple other factors beyond clinicopathologic staging in 131 I therapy decision making; (iv) recognize that the optimal administered activity of 131 I adjuvant treatment cannot be definitely determined from the published literature; and (v) acknowledge that current definitions of 131 I-refractory disease are suboptimal and do not represent definitive criteria to mandate whether 131 I therapy should be recommended.