Many patients with inflammatory bowel disease (IBD) have persistent symptoms and disease activity despite the best available medical or surgical treatments. These patients are commonly referred to as having difficult-to-treat IBD and need additional therapeutic strategies. However, the absence of standard definitions has impeded clinical research efforts and comparisons of data. Under the guidance of the endpoints cluster of the International Organization for the Study of Inflammatory Bowel Disease, we held a consensus meeting to propose a common operative definition for difficult-to-treat IBD. 16 participants from 12 countries voted on 20 statements covering various elements of difficult-to-treat IBD, such as failure of medical and surgical treatments, disease phenotypes, and specific complaints from patients. "Agreement" was defined as at least 75% consensus. The group agreed that difficult-to-treat IBD is defined by the failure of biologics and advanced small molecules with at least two different mechanisms of action, or postoperative recurrence of Crohn's disease after two surgical resections in adults, or one in children. In addition, chronic antibiotic-refractory pouchitis, complex perianal disease, and comorbid psychosocial complications that impair disease management also qualified as difficult-to-treat IBD. Adoption of these criteria could serve to standardise reporting, guide enrolment in clinical trials, and help identify candidates for enhanced treatment strategies., Competing Interests: Declaration of interests FDA has served as a speaker for Janssen, Galapagos, Sandoz, and Omega Pharma. MTA has served as a trainer or lecturer for Prime CME, Janssen Pharmaceuticals, Focus Medical Communications, Cornerstones Health, and Imedex; and as a consultant or advisor to Abbvie, Janssen, Gilead, Prometheus Biosciences, Takeda, UCB Biopharma SRL, Eli Lilly, Pfizer, Celsius, and Bristol Myers Squibb. AD has received research support or acted as a principal investigator for Abbvie, Dr Falk Pharma, Celgene/BMS, Gilead/Galapagos, Janssen, Biogen, and Takeda; has acted as a consultant for AbbVie, Abivax, Amgen, Boehringer Ingelheim, Celgene/BMS, Celltrion, Dr Falk Pharma, Ferring, Fresenius Kabi, Janssen, Lilly, MSD, Otsuka, Pfizer, Roche, Takeda, Tillotts, Pharmacosmos, and Vifor; and has participated in speaker bureaus for AbbVie, Amgen, BMS, Falk Foundation, Ferring, Galapagos, Janssen, Med Update, MSD, Pfizer, Roche, Takeda, Lilly, Tillotts, and Vifor. ID has served as a speaker, consultant, or advisory board member for Takeda, Janssen, AbbVie, Pfizer, Eli-Lilly, Ferring, Roche/Genentech, Cambridge Healthcare, Celgene/BMS, Falk Pharma, Ierative Scopes, Rafa Laboratories, Neopharm, Arena, Gilead, Galapagos, Celltrion, Sublimity, Sandoz, Abbott, and Athos Therapeutics. FM has served as a speaker and received honoraria from Abbvie, Arena, Biogen, Bristol-Myers Squibb, Falk, Ferring, Hospira, Janssen, Laboratórios Vitoria, Pfizer, Lilly, Merck Sharp & Dohme, Sandoz, Takeda, UCB, and Vifor. AFG has been a consultant for Abbvie, Amgen, Bristol Myers Squibb, Janssen, Lilly, Merck, Pfizer; and has received speaker fees from Abbvie and Janssen. VJ has received consulting or advisory board fees from AbbVie, Alimentiv (formerly Robarts Clinical Trials), Arena Pharmaceuticals, Asahi Kasei Pharma, Asieris, Bristol Myers Squibb, Celltrion, Eli Lilly, Ferring, Flagship Pioneering, Fresenius Kabi, Galapagos, GlaxoSmithKline, Genentech, Gilead, Janssen, Merck, Mylan, Pandion, Pendopharm, Pfizer, Protagonist, Reistone Biopharma, Roche, Sandoz, Second Genome, Takeda, Teva, Topivert, Vividion; and speaker's fees from AbbVie, Ferring, Galapagos, Janssen Pfizer Shire, Takeda, and Fresenius Kabi. MI has received speaker fees from Pfizer; has received funding from the National Institute for Health and Care Research, Birmingham Biomedical Research Centre at the University Hospitals Birmingham NHS Foundation Trust and the University of Birmingham; and received research grants from Pentax, Fujinon, and Olympus. GJM has served as advisory board member for AbbVie, Celgene, Celtrion, Ferring, Genesis, Hospira, Janssen, Millennium Pharmaceuticals, Merck Sharp & Dohme, Mylan, Pharmacosmos, Pfizer, Takeda, and Vianex; has served as a speaker for AbbVie, Angelini, Falk Pharma, Ferring, Galenica, Cenesis, Hospira, Janssen, Merck Sharp & Dohme, Omega Pharma, Takeda, and Vianex; has served as a consultant for Merck Sharp & Dohme and Takeda; and has received research support from AbbVie, Galenica, Genesis, Menarini Group, and Merck Sharp & Dohme. WR has served as a speaker for Abbott Laboratories, AbbVie, Aesca, Aptalis, Astellas, Centocor, Celltrion, Danone Austria, Elan, Falk Pharma GmbH, Ferring, Immundiagnostik, Mitsubishi Tanabe Pharma Corporation, MSD, Otsuka, PDL, Pharmacosmos, PLS Education, Schering-Plough, Shire, Takeda, Therakos, Vifor, and Yakult; has served as a consultant for Abbott Laboratories, AbbVie, Aesca, Algernon, Amgen, AM Pharma, AMT, AOP Orphan, Arena Pharmaceuticals, Astellas, Astra Zeneca, Avaxia, Roland Berger GmBH, Bioclinica, Biogen IDEC, Boehringer-Ingelheim, Bristol Myers Squibb, Cellerix, Chemocentryx, Celgene, Centocor, Celltrion, Covance, Danone Austria, DSM, Elan, Eli Lilly, Ernest & Young, Falk Pharma GmbH, Ferring, Galapagos, Gatehouse Bio, Genentech, Gilead, Grünenthal, ICON, Index Pharma, Inova, Intrinsic Imaging, Janssen, Johnson & Johnson, Kyowa Hakko Kirin Pharma, Lipid Therapeutics, LivaNova, Mallinckrodt, Medahead, MedImmune, Millenium, Mitsubishi Tanabe Pharma Corporation, MSD, Nash Pharmaceuticals, Nestle, Nippon Kayaku, Novartis, Ocera, OMass, Otsuka, Parexel, PDL, Periconsulting, Pharmacosmos, Philip Morris Institute, Pfizer, Procter & Gamble, Prometheus, Protagonist, Provention, Quell Therapeutics, Robarts Clinical Trial, Sandoz, Schering-Plough, Second Genome, Seres Therapeutics, Setpointmedical, Sigmoid, Sublimity, Takeda, Therakos, Theravance, Tigenix, UCB, Vifor, Zealand, Zyngenia, and 4SC; has served as an advisory board member for Abbott Laboratories, AbbVie, Aesca, Amgen, AM Pharma, Astellas, Astra Zeneca, Avaxia, Biogen IDEC, Boehringer-Ingelheim, Bristol Myers Squibb, Cellerix, Chemocentryx, Celgene, Centocor, Celltrion, Danone Austria, DSM, Elan, Ferring, Galapagos, Genentech, Grünenthal, Inova, Janssen, Johnson & Johnson, Kyowa Hakko Kirin Pharma, Lipid Therapeutics, MedImmune, Millenium, Mitsubishi Tanabe Pharma Corporation, MSD, Nestle, Novartis, Ocera, Otsuka, PDL, Pharmacosmos, Pfizer, Procter & Gamble, Prometheus, Sandoz, Schering-Plough, Second Genome, Setpointmedical, Takeda, Therakos, Tigenix, UCB, Zealand, Zyngenia, and 4SC; and has received research funding from Abbott Laboratories, AbbVie, Aesca, Centocor, Falk Pharma GmbH, Immundiagnostik, Janssen, MSD, Sandoz, and Takeda. DT reports consultation fees, research grants, royalties, or honorariaum from Janssen, Pfizer, Hospital for Sick Children (Canada), Ferring, AbbVie, Takeda, Atlantic Health System, Shire, Celgene, Lilly, Roche, ThermoFisher, and Bristol Myers Squibb. DTR has received grant support from Takeda, and has served as a consultant for Abbvie, Altrubio, Aslan Pharmaceuticals, Athos Therapeutics, Bellatrix Pharmaceuticals, Boehringer Ingelheim, Bristol-Myers Squibb, Celgene Chronicles, Corp/Syneos, ClostraBio, Connect BioPharma, Eco R1, Genentech/Roche, Gilead Sciences, Iterative Health, Janssen Pharmaceuticals, Kaleido Biosciences, Lilly, Pfizer, Prometheus Biosciences, Reistone, Seres Therapeutics, Takeda, Target RWE, and Trellus Health. LP-B reports personal fees from Galapagos, AbbVie, Janssen, Genentech, Ferring, Tillots, Celltrion, Takeda, Pfizer, Index Pharmaceuticals, Sandoz, Celgene, Biogen, Samsung Bioepis, Inotrem, Al-lergan, MSD, Roche, Arena, Gilead, Amgen, BMS, Vifor, Norgine, Mylan, Lilly, Fresenius Kabi, OSE Immunotherapeutics, Enthera, Theravance, Pandion Therapeutics, Gossamer Bio, Viatris, Thermo Fisher; grants from AbbVie, MSD, Takeda, Fresenius Kabi; and has stock options in CTMA. SG declares consulting fees from Pfizer, Janssen, AbbVie, Takeda, Bristol-Myers Squibb, Receptos, Celgene, Gilead, Eli Lilly, and Boehringer Ingelheim; and speaker fees from AbbVie, Janssen, Takeda, Ferring, Shield, and Falk Pharma. SD has served as a speaker, consultant, and advisory board member for Schering-Plough, AbbVie, Actelion, Alphawasserman, AstraZeneca, Cellerix, Cosmo Pharmaceuticals, Ferring, Genentech, Grunenthal, Johnson & Johnson, Millenium Takeda, MSD, Nikkiso Europe GmbH, Novo Nordisk, Nycomed, Pfizer, Pharmacosmos, UCB Pharma, and Vifor. All other authors declare no competing interests., (Copyright © 2023 Elsevier Ltd. All rights reserved.)