Biliary strictures of undetermined etiology pose a diagnostic challenge for endoscopists. Despite advances in technology, diagnosing malignancy in biliary strictures often requires multiple procedures. The Grading of Recommendations Assessment, Development and Evaluation (GRADE) framework was used to rigorously review and synthesize the available literature on strategies used to diagnose undetermined biliary strictures. Using a systematic review and meta-analysis of each diagnostic modality, including fluoroscopic-guided biopsies, brush cytology, cholangioscopy, and endoscopic ultrasound fine needle aspiration or biopsy, the American Society of Gastrointestinal Endoscopy (ASGE) Standards of Practice committee provides this guideline on modalities used to diagnose biliary strictures of undetermined etiology. This document summarizes the methods used in the GRADE analysis to make recommendations, while the “Summary and Recommendations” document contains a concise summary of our findings and final recommendations.