Investment to scale-up early infant diagnosis (EID) of HIV has increased substantially in the last decade. This investment includes physical infrastructure, equipment, human resources, and specimen transportation systems as well as specialized mechanisms to deliver laboratory results to clinics. The Global Plan Towards the Elimination of New HIV Infections Among Children by 2015 and Keeping Their Mothers Alive, as well as related international initiatives to prevent mother-to-child transmission of HIV and treat children living with HIV have been important drivers of this scale-up by mobilizing resources, creating advocacy, developing normative recommendations, and providing direct technical support to countries through the global community of international stakeholders. As a result, the number of early infant diagnosis tests performed annually has increased 10-fold between 2005 and 2015, and many thousands of infants are now receiving life-saving antiretroviral therapy because of this improved access. Despite these efforts and many success stories, timely infant diagnosis remains a challenge in many Global Plan countries. The most recent data (from the end of 2015) suggest a large variation in access. Some countries report that almost 90% of HIV-exposed infants are being tested; others report that the level of access has stagnated at 30%. Still, just over half of all exposed infants in Global Plan countries receive a test in the first 2 months of life. We discuss the key factors that are responsible for this scale-up of diagnostic capacity, highlight some of the challenges that have hampered progress, and describe priorities for the future that can help maintain momentum to achieve true universal access to HIV testing for children.