In Europe, sponsors must possess a compliant Paediatric Investigation Plan (PIP) when applying for marketing approval of drugs. The core deliverable is the ‘scientific part of the application’ structured according to the EMA's PIP guideline. The PIP should summarize relevant background information on the disease and drug, and use this to justify a paediatric development programme that covers the entire paediatric population. Depending on the type of drug and the relevance of the disease to the paediatric population, specific quality, safety, and/or efficacy measures may be proposed for all or part of the population. If measures are considered inappropriate for all or part of the paediatric population, then a waiver may be proposed but must be justified. If the paediatric development programme cannot be completed before submission of the adult application, then a deferral of the paediatric measures may be proposed but again this must be justified. In any case, a detailed timetable has to be provided and adhered to for any all measures being proposed. The main challenges for medical writers when writing a PIP are application of the guidance to the drug and disease in hand, and obtaining the appropriate input from the project team.