In this talk, I consider the validity of the classical theory of transport processes in collisional plasmas – that is, plasma in which the mean-free-path λ of constituent particles is short compared to the length scale L over which fields and bulk motions in the plasma vary macroscopically, and the collision time is short compared to the evolution time. Fluid equations are typically used to describe such plasmas, since their distribution functions are close to being Maxwellian. The small deviations from the Maxwellian distribution are calculated via the Chapman-Enskog (CE) expansion and determine macroscopic momentum and heat transport in the plasma. Such a calculation is only valid if the underlying CE distribution function is kinetically stable at collisionless scales. I will demonstrate that at sufficiently high plasma β, the CE distribution function can be subject to numerous microinstabilities across a wide range of scales, the most significant of which shall be characterized. Of specific note is the discovery of several previously uncharacterised microinstabilities whose growth rate in certain parameter regimes is large compared to other instabilities. Our work highlights that collisional plasmas can be kinetically unstable; in strongly magnetised CE plasmas, this occurs whenever β > L/λ. If kinetic instability arises, the determination of transport coefficients with the standard CE expansion is not valid; I will provide an example – the viscosity in an expanding plasma – of how revised calculations can be carried out, aided by kinetic simulations. The implications of these results for ICF experiments will be discussed, as will evidence for discrepancies from standard models of collisional plasma transport arising in recent laser-plasma experiments on the National Ignition Facility.