This book provides a critical review of research in mathematics education published in or about the Australasian region in the four years from 2020 to 2023. Research in Mathematics Education in Australasia 2020-2023 (RiMEA 2020-2023) is the eleventh edition of the four-yearly review of mathematics education research in Australasia. It is compiled by the Mathematics Education Research Group of Australasia (MERGA). It is primarily focused on research from Australia, New Zealand, and Singapore but also includes research from other Southeast Asian countries and the South Pacific. Although each edition of RiMEA is shaped by the preceding volumes, each new edition evolves in response to events coinciding with each new review period. Following an introduction by the editors, RiMEA 2020-2023 will contain a reflection chapter authored by the editors of the previous edition, 'Research in Mathematics Education in Australasia 2016-2019,' on how research in mathematics education in the Australasian region has progressed over the four years since. This book provides a comprehensive critical review of research literature in the Australasian region on significant topics published within the review period. It serves as a resource for researchers and promotes quality research in the Australasian region. Furthermore, it provides an introduction to mathematics education research in the Australasian region for Ph.D. candidates, early career researchers, and other researchers beginning a new field of research.