Background: The approach to adenocarcinoma in situ (AIS) is challenged by diagnostic complexity, limited high-quality evidence, and heterogeneous guidance. Methods: We conducted a narrative comparative review of global guidelines/recommendations (2012–2025; search updated 1 October 2025), extracting data across 38 topics related to AIS management and classifying indications into five categories of coverage/consensus. Results: Twenty documents from national or supranational bodies were included. A cross-guideline consensus emerged on eight core items (colposcopy for any glandular cytologic abnormality; role of HPV test; mandatory histologic confirmation; excisional treatment for histologic AIS; re-excision when margins are involved; criteria and type of hysterectomy; and expert/centralized management). Operational variability emerged in the excisional technique, pathways for discordant results, management during pregnancy, and follow-up protocols. Divergent guidance was most evident for indications to endocervical sampling, criteria for conservative management, and the need for hysterectomy after completed childbearing. Limited-coverage consensus involved the technique of initial histologic sampling, endometrial assessment, and pathways for cytology subtypes. Several areas remained unaddressed. Conclusions: While the essential management of AIS is well defined, uncertainty increases when treatment must be personalized. A core outcome set and rigorous multicenter studies are needed to reduce heterogeneity and enable truly evidence-based personalization.