INTRODUCTION: Recent new advances in myoclonus characterization and etiology justify an update of the 40-year-old respected classification of myoclonus proposed by Marsden, Hallett, and Fahn. New advances include genetic studies and clinical neurophysiology characterization. METHODS: The IAPRD appointed an expert panel to develop a new myoclonus classification. The Delphi Method of consensus determination was employed using a panel of fifteen international experts in myoclonus. In an in-person meeting, an Axis approach, previously used for dystonia and tremor was ratified by the panel: Axis I included clinical and neurophysiology features, Axis II included etiology categories. As a unique part of our Axis approach, Clinical Neurophysiology was included as Axis Ib. The first Delphi survey round queried agreement on major headings in Axes Ia and Ib, myoclonus clinical syndromes, and Axis II. In the second round, the full expert panel was surveyed on constituents and specific characteristics of each feature that had consensus in the first round. RESULTS: In the first round, the percentage of agreement for the fifty-three out of the 56 items was greater than 60.0 %, indicating strong consensus among expert panel members. In the second round, for Axis Ia, Axis Ib, and Axis II, strong agreement was also achieved. For both rounds, Physiological Myoclonus had the lowest agreement. Comments from the whole panel were incorporated into the consensus results. CONCLUSION: This Myoclonus Classification, which reached consensus using the Delphi Method, will facilitate a collaborative effort among myoclonus investigators to find better diagnostics and treatment for myoclonus patients.