Development in the field of enzymatic degradation of plant biomass has potential to drastically improve production of biofuels and biomaterials. This thesis focuses on two different types of enzymes: Lytic polysaccharide monooxygenases (LPMOs) and glycoside hydrolases (GHs) from the CAZy family GH53. Enzymes from the GH53 family degrade parts of pectin, which is often found in the primary plant cell wall. We have structurally and biochemically characterized the most hyperthermostable GH53 enzyme to date, hereby elucidating structural features correlated to thermostability and degradation profile. This information was further extrapolated to all GH53 sequences in the CAZy database, showing trends for eukaryotes, bacterial and archaeal origin. Initial development of an activity assay using dynamic light scattering was conducted with GH53 enzymes acting on lupin galactan. It is of interest to further develop the method to include other substrates and enzymes. LPMOs are enzymes capable of oxidatively cleaving of the glycosidic bond utilizing a copper atom bound in a histidine brace. They are capable of degrading recalcitrant polysaccharides and exhibit an ability to boost GH activity. However, their mechanism is still heavily debated. We have probed details of the primary and secondary copper-coordination sphere using high resolution data sets of model AA9 LPMO from Lentinus similis produced in E. coli (LsAA9A_Ec) and a mutational study the copper transporter CopC from Pseudomonas fluorescens (PfCopC). PfCopC also contains a histidine brace but is not enzymatically active. Variants aimed at changing the substrate specificity of LsAA9A_Ec were also characterized structurally and with respect to stability and oligosaccharide binding. This thesis also contains structural characterization of novel LPMOs. The structure of the AA10 LPMO from Lactiplantibacillus plantarum (LpAA10), a bacterium often found in the human gut, indicated a weaker binding of copper compared with many other LPMOs. Based on a bioinformatic study of AA10 sequences it was elucidated that LpAA10 most likely is chitin active. The first experimental AA16 enzyme structure was also obtained. The AA16 from Myceliophthora thermophila showed a boosting effect on AA9s from the same fungus but not on those from different fungi.