The Family 7 processive cellulases are the basis of many enzyme cocktails for lignocellulosic biomass conversion. Despite their importance, a detailed mechanistic understanding of the Family 7 enzymes remains elusive. Here we present recent results illustrating our ongoing efforts to construct a molecular-level model of the action of a Family 7 cellulase, using the Trichoderma reesei Cel7A enzyme as the basis for study. The three sub-domains of Cel7A, namely the Family 1 carbohydrate-binding module, the O-glycosylated linker peptide, and the catalytic domain are studied independently to ascertain isolated structure-function relationships. The knowledge gained from studies of the individual domains is vital in developing a quantitative, mechanistic model of the processive action of Cel7A. Additionally, the free energy cost to decrystallize cellulose is an essential part of this model; thus, we also present a complementary study in which we measure the molecular-level basis for cellulose recalcitrance, which Cel7A (and other cellulase enzymes) must overcome to degrade the plant cell wall.