This chapter gives an overview of threeFriction importantInertia considerations in HopkinsonHopkinson bar testing. Firstly, as in any compressionCompression experiment, compressionCompression Hopkinson bar experiments require appropriate lubrication of the interfaces between the specimen and the anvils in order to reduce the shearShear force on the specimen as it expands. Secondly, testing at high strain rateStrain rate requires rapid accelerations of the specimen. One manifestation of this is longitudinal stress waveStress wave oscillation within the specimen; however, even if the specimen is in static equilibrium, there are inertial effects associated with the axial and radial acceleration of the material as it deforms. Finally, because HopkinsonHopkinson bar experiments do not have any form of closed loop control, there is variation of the strain rateStrain rate in the specimen, which depends on both the incident pulse and the nature of the specimen response. A short discussion of how the strain rateStrain rate varies, and how this variation can be minimised, is given. Much of the discussion about inertiaInertia and frictionFriction is based on a recent book chapter by Siviour and Walley (Inertial and frictional effects in dynamic compression testing, in the Kolsky-Hopkinson Bar Machine, Springer Nature, pp. 205–248, 2018), in which more detail about these subjects can be found.