BES, the Beijing Spectrometer, began its first groundbreaking physics run, thirty years ago, in 1989. This is the first high energy physics experiment in China, and has been unique throughout the world for its thorough and extended coverage of the tau and charm energy region. Since then, the BES detector has undergone steady improvements, upgrading to BESII in 1998 and to BESIII in 2008. Over the same period, the collaboration has expanded from 150 members, across 10 institutions in China and the United States, to about 500 members, across 72 institutions and 15 countries. The physics program, too, has extended from light hadron spectroscopy, tau, and charm physics to the discovery of exotic charmonium-like states, precision tests of the Standard Model of particle physics, and searches for new physics beyond the Standard Model.This special volume collects the proceedings of the symposium held at the Institute of High Energy Physics, Beijing, in celebration of the 30-year span of achievements and progress at the BES, BESII, and BESIII experiments. Written by many leaders of the BES collaborations, these proceedings document the early days of the BES experiments, important milestones, and the future physics program at BESIII.