This is a cohort study with a 1 arm intervention group, without a control group. Patients included in this study will be invited to use a mobile application. The content and functionalities of this application are described in the intervention section.

Patients will use a mobile application for ±6months (exact period depends on interval of biologic treatment) with the following functionalities:

• Personal interactive timeline to prepare for biologic treatment with reminders for blood tests, a questionnaire to exclude contra-indications for biologic treatment (e.g. current infection) and a message from the gastroenterology nurse when blood tests results and the questionnaire have been checked. Only in case of abnormal results or answers patients will be contacted by telephone by their gastroenterology nurse, which is currently standard care.
• Information about the patients' diagnosis and biologic treatment.
• General information on e.g. IBD treatment, vaccinations, frequently used medical terms, preparing for outpatient visits, what to do in case of disease symptoms.

Patients will fill in a questionnaire to measure study outcomes at baseline and at the end of the study period.

All patients will be asked to complete questions about satisfaction with the mobile application, the information in the app and the user-friendliness of the app. This will be measured with a 7-point likert scale after using the application for ± 6 months. We will also ask patients about their overall satisfaction of care before and after implementation of the application using a visual analogue scale (VAS) scale 0 - 10.

Use will be monitored with log data of the application. We will look at frequency of use of the application.

The adherence of patients to reminders will be evaluated by checking time of blood tests as recorded in the electronic medical record and log data from administered questionnaires.

After ± 6 months, health care professionals will be asked to fill in a questionnaire to measure their experiences with the application, experience with monitoring the questionnaire, satisfaction, organizational advantages/disadvantages for example time investment, efficiency of work processes. This will be measured with a 7-point likert scale after using the application for ± 6 months. We will also ask care providers about their overall satisfaction with the application using a VAS scale 0 - 10.