First adopted in 1980, the OECD Privacy Guidelines are the first internationally agreed-upon set of privacy principles. They are framed in concise, technology-neutral language and have significantly influenced legislation and policy in OECD member countries and beyond. In 2018, the OECD initiated a comprehensive review of the Privacy Guidelines, which included a survey of Adherents, an ad hoc group of experts, and several workshops to explore the main challenges for privacy and personal data protection in an ever-evolving digital environment. This report presents the review's findings, confirming the continued importance and relevance of the Privacy Guidelines. However, it also highlights persistent and emerging implementation challenges and provides recommendations for addressing them.