Glucuronoyl esterases  (GEs) are α/β serine hydrolases from Carbohydrate Esterase family 15 (CE15) which cleave an ester linkage that connects lignin to glucuronyl xylan, an important linkage contributing to biomass recalcitrance. In recent years, we have been exploring the structure-function relationships of several CE15 members, particularly focused on bacterial members and those in species encoding multiple CE15 members [1]. Our research indicates that bacterial enzymes exhibit greater diversity compared to fungal members, often featuring large inserts near the active site, likely affecting substrate interactions and specificities. Crystal structures with ligands, as well as biochemical and computational studies, have further identified key residues and potential rate-limiting steps in the catalytic process [2]. While there is considerable evidence supporting the role of many CE15 enzymes as GEs in degrading lignocellulosic lignin-carbohydrate complexes (LCCs), our published work [3, 4] and further studies have revealed several unusual CE15 members in both fungi and bacteria. These CE15 proteins cannot be confidently identified as GEs due to their unique activity profiles, sequences, 3D structures, and genetic contexts. Presented will be our recent and ongoing work into gaining a better understanding of the family as a whole with particular attention given to possible new biological functions for these unusual CE15 members beyond decoupling lignin-glucuronoyl xylan linkages.