Performing rheological measurements of mortar and concrete is not a straightforward task as many challenges can alter or invalidate the outcome of a rheological experiment. This chapter summarizes the most common challenges for flow curve measurements, which are the type of flow behavior, achieving the reference state, plug flow, shear and gravity-induced particle migration, hydrodynamic pressure, heat of vaporization, correct choice of rheological transformation equations and model, air, and wall effects. Some of these challenges are also detailed separately for static yield stress measurements. For each challenge, the physical background, consequence on the measurement outcome and any detection or prevention strategy are described. To adequately perform rheological measurements, all challenges need to be addressed, which can be a daunting task as some prevention strategies can increase the risk for a different challenge to affect the measurement. Developing a suitable measuring and analysis procedure is a critical task to the success of rheological measurements of mortar and concrete.