The role played by the porous nature of the packing material in the hysteretic behavior of trickle-bed reactors (TBRs) is presented based on a new framework that incorporates the current understanding of fluid flow in TBRs, concepts of participating and nonparticipating particles, and principles of liquid spreading on porous and nonporous substrates. A method to characterize the extent of hysteresis is also presented. The framework is applied to reported experiments (Ravindra, P. V.; Rao, D. P.; Rao, M. S. Ind. Eng. Chem. Res. 1997, 36, 5133-45) and is shown to be able to explain the difference in the hysteretic behavior of porous packings and of nonporous packings (comparable particle size) under varying startup conditions and numbers of cycles. In addition to providing a basis for the general framework within which hysteresis in TBRs should be studied, it provides explanations to specific questions such as (1) the existence of hysteresis in porous packings and its absence in nonporous packings under similar conditions and (2) when to expect open-loop or closed-loop hystersis. It is also a good illustration of how a framework, which is based on pore levels, can explain reactor level complex phenomena like hysteresis. It is expected that this work will enhance our understanding about the variations of the hysteretic behavior as well as hydrodynamics in TBR. In the absence of a data bank in the literature, the proposed framework has been validated with available limited data.