⁃ Male or female, aged at least 18 years old.

⁃ Diagnosis of inflammatory bowel disease according to the ECCO criteria for at least 3 months:

∙ moderately to severely active CD (Crohn's disease)

‣ moderately to severely active UC (Ulcerative colitis)

⁃ Patients had received conventional therapy for active UC (corticosteroids alone or in combination with thiopurines and 5-aminosalicylates) or CD (corticosteroids and/or immunomodulators) but had not responded despite an adequate course of therapy.

⁃ Patient has active CD or UC with at least one objective sign of disease activity on biology, endoscopy or imaging.

⁃ Initiation of infliximab CT-P13 as part of standard of care.

⁃ Patient suffering from anal suppuration related to CD can be included.

⁃ Person who has received full information about the organization of the research, who has not objected to his or her participation and to the use of his or her data.

⁃ Person affiliated to or beneficiary of a social security plan.

⁃ ► Inclusion criteria for Women of Childbearing Age:

• Women of childbearing age should consider the use of appropriate contraception to prevent pregnancy and continue its use for at least 6 months after the last infliximab treatment. Women should choose one of the following methods of contraception:

• Combined hormonal contraception containing estrogen and progesterone (oral, IUD, transdermal, injectable) combined with ovulation inhibition.

• Initiated at least 30 days before Baseline Day 1.

• Progestin-only hormonal contraception (oral, injectable, implantable) associated with ovulation inhibition initiated at least 30 days before the first injection.

• Bilateral tubal occlusion (can be performed by hysteroscopy, provided that hysterosalpingography confirms the success of the procedure).

• Intrauterine device (IUD).

• Practicing true abstinence, defined as: abstaining from heterosexual intercourse when this corresponds to the subject's preferred and usual lifestyle (periodic abstinence \[e.g. calendar method, ovulation method, symptothermal method, post-ovulation methods\] and withdrawal are not acceptable)

‣ Inclusion Criteria for Women Not of Childbearing Age:

• Women do not need to use contraception during or after treatment with study drug if they are considered not of childbearing age due to one of the following situations:

• Premenopausal women with permanent infertility following hysterectomy, bilateral salpingectomy or bilateral oophorectomy.

• Postmenopausal women

• Age \> 55 years without menstruation for 12 months or more without alternative medical cause.

• Age ≤ 55 years without menstruation for 12 months or more without alternative medical cause AND a folliculostimulin (FSH) level \> 30 IU/L.