Purpose: This study proposes the Lamella Ostium Extent Mucosa (LOEM) system as a compact and user-friendly classification for endoscopic sinus surgery (ESS), based on surgical bone extension and mucosal management, aiming to resolve inconsistencies in describing surgical techniques and extension levels, and to enhance comparability of outcomes in chronic rhinosinusitis (CRS). Methods: LOEM uses a lettering system representing a specific topographical level: L identifies the lamellae, O the ostia, E the opening of the sinus walls, and M the mucosal approach. Eleven CRS surgical cases were independently evaluated by seven rhinologists following a Delphi method in two consecutive rounds. Consensus was assessed using Cohen's kappa. Results: A substantial agreement was found among the experts (κ = 0.77) in the first round, although the M item only showed fair agreement (κ = 0.37). Clarifications for this item were given in the second round, after which, the overall agreement increased to κ = 0.81 and to κ = 0.79 for the M item. A decrease in agreement from substantial to moderate for O and E items in the second round was found. Test–retest analysis showed an almost perfect agreement (92.96%, κ = 0.82). In this study, a web-based app is provided to assist with the regular use of the LOEM system. Conclusions: The LOEM system provides a compact, comprehensive code for ESS, integrating anatomical and functional aspects to represent surgical techniques described so far. This system may be suitable for facilitating communication between surgeons and collecting robust labeled data, hopefully leading to further standardization and validation of surgical approaches in future CRS studies.