This chapter examines the issue from the perspective of a Belgian overseer. The importance of 'big data' in relation to intelligence became apparent years ago after the Echelon programme was revealed and after the Snowden revelations. The Committee is a permanent, independent body currently composed of 12 staff members, initially only responsible for reviewing the activities and functioning of the two Belgian intelligence services. Both before and after the 9/11 attacks, the Belgian intelligence services made different proposals to obtain more powers and more resources. The Belgian intelligence agencies only have had the legal power since 2010 to use intrusive intelligence methods: tapping, acquisition of telecommunications metadata, observations in houses or other private places, opening of post mail, hacking of IT-systems, requesting financial data. 'The ongoing evolution of the technological, budgetary and legal resources available to police and intelligence services must be accompanied by the improvement of the control of these services'.