Over the past two decades, several two-tier multiple-choice diagnostic tests in science at a variety grade levels have been reported in the extant literature from several countries. This review summarises these studies, provides an overview of the methodology for their construction, presents two examples of typical items, and lists studies published with two-tier tests. The majority of these studies have been conducted with relatively small numbers of students in one school, college, or university, although there are exceptions. What distinguishes the research reported in the articles in this Special Issue is that the Taiwanese two-tiered tests for the National Science Concept Learning Study were designed to identify the scientific conceptions of students from large national samples using random sampling procedures similar to those found in studies such as Trends in Mathematics and Science Studies and Programme for International Student Assessment. The article concludes with implications for the use of two-tier tests for pedagogical practice and research. (Contains 1 table and 3 figures.)