I figured out the chronological order for the films a while ago and posted it on another site. I’m copying it here mainly for my own convenience.

  1. Watch the first 8 minutes of Underworld: Evolution. Stop when it says, “Screen Gems and Lakeshore Entertainment.” This portion is dated to the year 1202.
  2. Watch Underworld: Rise of the Lycans. Selene’s narration in the first minute of the film is misleading: the film starts in the early 13th century, and the main portion of the film is set in the early 15th century. Stop or mute the film quickly at the end (time 1:22:33 on the DVD), when the screen fades to black and you start to hear, “but let me tell you a little something...” The video won’t contain any spoilers, but the audio will. You can unmute the audio when the credits start.
  3. Watch Underworld: Endless War, parts 1 and 2, which are set in 1890 and 1967.
  4. Watch Underworld, set in or near 2003.
  5. Watch the rest of Evolution. The flashback 55 minutes in predates the main events of Rise of the Lycans by a couple decades, but it’s too short to separate it from the film and watch it in chronological order.
  6. Watch Endless War, part 3, set in 2012.
  7. Watch Underworld: Awakening.
  8. Watch Underworld: Blood Wars.