These proceedings are a written record of the research presented at the 41st annual meeting of the North American Chapter of the International Group for the Psychology of Mathematics Education (PME-NA) held in St. Louis, Missouri, November 14-17, 2019. This year's conference theme is "...against a new horizon." The papers comprise 67 research reports, 184 brief research reports, 126 posters, and 13 working groups. Chapters include the following: (1) Plenaries; (2) Curriculum, Technology, and Assessment; (3) Early Algebra, Algebra, and Number Concepts; (4) Equity and Justice; (5) Geometry, Measurement, Statistics, and Probability; (6) In-Service Teacher Education and Professional Development; (7) Instructional Leadership, Policy, and Institutions/Systems; (8) Mathematical Knowledge for Teaching; (9) Mathematical Processes; (10) Precalculus, Calculus, and Higher Mathematics; (11) Pre-Service Teacher Education; (12) Student Learning and Related Factors; (13) Teaching and Classroom Practice; (14) Theory, Research Methods, and Miscellaneous Topics; and (15) Working Groups. [These proceedings were co-published by University of Missouri, St. Louis. Individual plenary and research papers are available in ERIC.]