For PC, with PS4 and Xbox One to follow at a later date. As per the headline, and rules that mandate that any release with the word collection in the title has to feature everything, the XCOM 2 Collection brings all the XCOM 2 into one neat package. Including the 2016 original, all DLC, plus the 2017 expansion, XCOM 2: War of the Chosen.

Here's the full list of what's included.

XCOM 2 – Aliens rule Earth, promising a brilliant future for mankind while secretly hiding a sinister agenda. As the leader of a guerrilla force facing impossible odds, you must ignite a global resistance to eliminate the alien threat and save the human race from extinction.

• XCOM 2: Resistance Warrior Pack – Customize your squad of resistance fighters with a set of bonus outfits and head gear, as well as custom armor and face camo. Instantly unlock a survivor of the old war as a new recruit in your barracks.
  
• XCOM 2: Anarchy’s Children – This rebellion-themed content pack introduces more than 100 new exotic customizations for the entire arsenal of armors available to your XCOM soldiers. These options are purely cosmetic and do not alter the stats of a soldier.
  
• XCOM 2: Alien Hunters – Transform the soldiers of XCOM into an elite alien hunting squad with impressive new weapons and armor to face off against new alien Rulers that will pursue your squad across an entire campaign. Additional cosmetic upgrades to soldiers and the Avenger are included, as well as a new epic mission where Central Officer Bradford leads a squad with the guidance of an old friend.
  
• XCOM 2: Shen’s Last Gift – Investigate ADVENT’s “Lost Towers” facility where Chief Engineer Lily Shen accompanies your squad in search of her late father’s secretive final project. Discover a unique new soldier class complete with powerful new combat abilities, strategy mechanics, and customization options.

XCOM 2: War of the Chosen - The XCOM 2: War of the Chosen expansion adds extensive new content in the fight against ADVENT when additional resistance factions form in order to eliminate the alien threat on Earth. In response, a new enemy, known as the “Chosen,” emerges with one goal: recapture the Commander. The expansion includes new Hero classes to counter the “Chosen”, new enemies, missions, environments and increased depth in strategic gameplay.

Definitely something to consider if you haven't played the excellent XCOM 2 yet. But seeing as the XCOM 2 Collection is currently $99.99 USD on Steam you may want to hold off until it's on sale.