This chapter introduces the fundamental material properties that govern the behaviour of bulk solids during storage, flow, and handling operations. It provides a structured overview of established laboratory testing methods used to characterise bulk solids under conditions representative of industrial practice. Key parameters examined include flow functions for instantaneous and time-dependent storage, internal and wall friction properties, bulk density, permeability, and critical dimensions associated with arching and ratholing. Emphasis is placed on the principles and application of shear testing, with detailed discussion of the direct shear test and reference to alternative shear, biaxial, triaxial, and flowability test methods. The influence of material variables such as moisture content, particle size distribution, consolidation history, surface roughness, vibration, temperature, and ageing effects is systematically addressed. In addition, methods for evaluating wear, dustiness, and permeability are outlined. The material presented forms a fundamental basis for the analytical design of reliable and safe bulk solids storage and handling systems.