In 2021, MIT researchers made advances toward fusion energy, confirmed Stephen Hawking's black hole theorem, developed a Covid-detecting face mask, and created a programmable fiber. All were among the year's top research stories on MIT News. The year's popular research stories include a promising new approach to cancer immunotherapy, the confirmation of a 50-year-old theorem, and a major fusion breakthrough. Despite the pandemic's disruptions, MIT's research community still found a way to generate a number of impressive research breakthroughs in 2021. In the spirit of reflection that comes with every new orbit around the sun, below we count down 10 of the most-viewed research stories on MIT News from the past year.