Engineering for nostalgia: Building a personalized "On This Day" experience

One year ago, we launched On This Day to make it easier to relive and share memories on Facebook. Since launch, On This Day has been used by hundreds of millions of people globally. Because memories are so personal and unique, we wanted to make sure On This Day shows people the memories they most likely want to see and share, especially when it comes to the memories they see in News Feed. Specifically, over the past year, we focused on three areas to optimize the product experience: user experience research, filtering, and ranking. To better understand what types of memories are best to show people in News Feed, we listened to feedback from people through UX research. In these sessions, we learned just how complex memories can be.