Brown dwarfs are the latest discovered population on the HR diagram. They formed like stars but appearing like gaseous planets, thus bridging the gap between stars and planets. I will briefly introduce the research history of brown dwarfs and summarize the properties of known brown dwarfs. Then, I will explain the new discovered substellar transition zone formed by transitional brown dwarfs, and discuss the difference between brown dwarfs and exoplanets. At the end, I will show some discoveries of new L subdwarfs from Gaia.