This book presents the work of the RILEM TC 266-MRP, whose purpose was to enhance the reliability of rheological measurements performed on cement-based materials. It makes users more aware of potential sources of errors in the measurements, and provide guidelines on how to observe, counteract or eliminate the errors. Improving the reliability of rheological measurements will further enhance the use of rheology to investigate different aspects of the fresh properties of cement-based materials. After an introduction into mix design and applications, the book delivers a comprehensive overview of rheology definitions, behavior, and parameters; rheometers; measuring and analysis procedures; difficulties and challenges during measurements; relationships with specific empirical tests; and the behavior of concrete near a surface. This report on the measurement of rheological properties of complex materials such as concrete enables readers to understand the applicable concepts of rheology, and address the challenges on the measuring procedures, the rheological models and some errors and limitations of rheometers used.