On 25 May 2021, the Grand Chamber of the European Court of Human Rights handed down its decision in Big Brother Watch and Others v. the United Kingdom. The Grand Chamber, as the Chamber before it, ruled that some aspects of the surveillance regime of the United Kingdom violated Article 8 of the European Convention of Human Rights. At the same time, however, the Grand Chamber recognized that mass surveillance programs are of vital importance to identifying threats to the national security of States parties to the Convention. This paper analyses some of the most critical aspects of the Grand Chamber’s ruling, highlighting how the Grand Chamber, despite some procedural guarantees to protect the right to privacy, essentially continues to recognize a wide margin of appreciation regarding the measures to be used.