The purpose of the study is to assess whether a proactive therapeutic drug monitoring strategy, introduced early during treatment, improves Infliximab (IFX) durability, efficacy and safety in children and young adults with inflammatory bowel disease. Patients with an indication to receive IFX, based on current clinical practice recommendations, will receive the drug either based on IFX concentrations determined before every IFX infusion, starting from the third infusion, or at standard dosing. Approximately 90 patients will be included in this research study. Patients enrolled will be in the study for approximately 12 months.