Assassin's Creed series owned and produced by Ubisoft.

Based in a world where killers are, for once, the good guys, Assassin's Creed is the long, winding tale of a perpetual war between two factions - Assassins and Templars - who fight over secrets of the long-past. Originally delving into the genetic memories of assassin Desmond Miles and looking back in time, Assassin's Creed has become an historic tour de force that hops from time period to time period, ever focused on stealth kills, a variety of historical figures, and leaping into piles of hay.

Several of the Assassin's Creed games contain sequences featuring characters from the modern day who are looking back at past events. Playing the games chronologically will give you their historical order, without taking the modern day sections into account, while playing by release order will put them in modern day order. (Which is probably how you should play them, but it's up to you.) Any DLC released for the games should be played after the main game is complete.

Games that are not considered canon - or which are no longer available to play - are under Release Order only. They are marked as such in case you want to play through the modern day storyline while ignoring items that don't contribute to the larger story.

The Assassin's Creed franchise also includes a number of films and comics. Several of the animated films are canonical, and are included in the chronology. The rest are included under Release Order. (Comics will be added soon.)

In-Universe Chronological Order - The Past
Release Order (video games)
Release Order (films)