Computational fluid dynamics (CFD) is a tool that is becoming more realistic for use in the description of the detailed flow fields within fixed beds of low tube-to-particle diameter ratio (N). The motivation for the use of CFD is presented by reviewing the current state of fixed-bed reactor modeling, with an emphasis on the treatment of the description of fluid flow within the bed. Challenges in the use of CFD for fixed beds of particles are treated here, selected results are presented for N = 2 and N = 4, and potential uses of the simulation information in design models for fixed-bed reactors are discussed.