In this chapter we aim to explain the principles and evolutions of the testing and type approval of the GSM Mobile Equipment (ME). After having recalled the context at the end of the 1980s (paragraph 17.2), we outline the technical background (paragraph 17.3) and we explain the first step of the type approval, i.e. the ‘‘interim type approval’’(paragraph 17.4). Then we describe the TBR regime (paragraph 17.5) and how it evolved to cope with phase 2 (paragraph 17.6) and phase 21 (paragraph 17.7)..