Countless people made significant contributions to the four-year pioneering effort required to develop the TIMSS 2019 Problem Solving and Inquiry Tasks. Mathematics and science assessment specialists contributed the creative ideas underlying the tasks, in particular, Ray Philpot (ACER), Mary Lindquist (NCTM), Kathleen Scalise (ETS and University of Oregon), and Emily Jones (NFER). The individuals responsible for eTIMSS in the participating countries conducted special pilots, an ambitious field test, and participated in numerous reviews to inform this new endeavor. The TIMSS mathematics and science coordinators, Kerry Cotter and Victoria Centurino, spent many hours on the iterative process of producing and revising the tasks, receiving invaluable support from the international experts comprising the TIMSS 2019 Science and Mathematics Item Review Committee (SMIRC), the talented graphic designers at the TIMSS & PIRLS International Study Center, and dedicated computer specialists at IEA Hamburg.