The CIPM Mutual Recognition Arrangement (CIPM MRA) has now been signed by the representatives of 101 institutes and covers a further 153 institutes designated by these signatories. These come from 57 Member States, 40 Associate States and Economies of the CGPM, and 4 international organizations. Through it the national metrology institutes can demonstrate their measurement abilities and publish internationally recognized statements of their so-called calibration and measurement capabilities (CMCs). All the data are openly available in the CIPM MRA database (the KCDB), which has become an essential reference for the NMIs themselves, accredited laboratory community as well as a small number of high end industrial and other organisations. In this paper we review the situation that led to the development of the CIPM MRA, identifying the three main drivers: the challenges of regulators wanting traceability to the national NMI in an increasingly globalised world; the emergence of a laboratory accreditation and with it the need for laboratories to demonstrate metrological competence; and finally the emergence and strengthening of the Regional Metrology Organizations (RMOs). The paper also addresses the CIPM MRA structure, its operational mechanisms and impact, and concludes with some speculative remarks as to how it might evolve in the future.