Laser fusion hydrodynamics calculations include both the solution of the plasma hydrodynamics equations and transport equations for various nonthermal particles. The solution of the hydrodynamics equations is usually a combination of an explicit technique for the hyperbolic equation-of-motion and an implicit method for parabolic temperature equations. Transport equations are solved using fully implicit techniques to allow their time step to be as large as the time step used in the solution of the hydrodynamics equations. Multigroup flux-limited diffusion theory is often used to model the time-dependent transport problem. In this method, the diffusion coefficient is “adjusted” to provide a physically plausible result in the free streaming limit. The energy dependence of the distribution function is modeled using multigroup theory. Another method of solving the transport problem, time-dependent particle tracking, approximates the trajectory of the charged particles as straight lines, from creation to thermalization. This simple method accurately describes the slowing down of thermonuclear reaction products, while the flux-limited diffusion technique is more applicable to the transport of electrons and photons.