The challenges in teaching and learning of biological evolution continue to be documented (NAS, 2008). Developers of science standards continue their work to increase emphasis on evolution. Although gains have been made, many K-12 science curricula focus on microevolution (i.e., natural selection, genetic drift), and a more limited effort is in place to provide exposure to macroevolution (i.e., speciation). Many of the public's fundamental questions concerning evolution actually stem from macroevolutionary changes. This research involved the development and psychometric evaluation of the Measure of Understanding of Macroevolution (MUM), an assessment of college undergraduate understanding of the scientific portrayal of macroevolution. The MUM comprises 27 multiple-choice items and 1 free-response item. The authors achieved content validity based on feedback from professional biologists and evolution educators. The MUM was field tested with 3 unique cohorts of undergraduate students (N = 795). The validity and reliability analyses indicate that the MUM effectively, consistently, and accurately measures students' understanding of macroevolution. (Contains 4 tables and 7 figures.)