This study conducted by Milieu was carried out for the Commission’s Directorate-General for Migration and Home Affairs. The aim was to provide an independent evidence-based analysis of the current legal situation and practical approaches regarding retention of and access to electronic communications non-content data (also known as metadata) for law enforcement purposes in ten selected EU Member States: Austria, Estonia, France, Germany, Ireland, Italy, Poland, Portugal, Slovenia and Spain. The study compares the practices, needs and challenges of electronic communications’ service providers (ESPs) and Over-the-Top service providers (OTTs) on the one hand and law enforcement authorities (LEAs) on the other through extensive desk research and targeted stakeholder consultations.