Physical Review B is celebrating its 50th anniversary in 2020. The journal emerged out of its revered parent, The Physical Review, in response to the explosive growth of specialized physics content. It has excelled in front-edge coverage of condensed matter and materials physics research. As part of the celebration, in 2020 the editors are presenting a Milestone collection of papers that have made lasting contributions to condensed matter physics. Selection of papers of such importance is not an easy task. It is inevitable that some very important work will not be featured because of the abundance of gems in the treasure trove of the largest journal for physics. The Milestones will be highlighted on the journal website and in social media throughout the year.