World War Z is a cooperative game by design, and having a fully kitted-out party loaded to the gills with perks can make even the most obnoxious challenges a breeze. Playing with friends is simple, though those looking to create a cross-platform party will be disappointed.
Opening the Social Menu in World War Z will allow you to invite anyone on your Friend’s List to your party.
The social menu can be accessed at any time outside of a mission in World War Z to invite friends into your party. Click the appropriate hotkey/button (or the empty portraits on PC) and you’ll be given the Invite option. Bear in mind that only friends that are online and playing World War Z will show up, so if your buddies have yet to login they won’t appear in this list.
Additionally, PC players cannot invite Xbox players, or vice-versa. It’s a strange omission, considering the platforms have crossplay enabled by default, so if you wanna play cross-platform with your friends you need to queue at the same time for the same mission (at the same difficulty) and pray for the best. PlayStation 4 players currently do not have crossplay as an option whatsoever, so don’t expect to play with your cross-platform friends until the feature is added (hopefully with cross-platform parties enabled).
That said, teams are limited to four players in World War Z, and you can play any game mode you want together. As a bonus, if someone in your party owns the new Marseilles missions they can host them for everyone else, regardless if the other players own the content or not. This only works with private parties, however, so if you opt to play with others via matchmaking then you won’t be able to play the new DLC unless you own it. DLC guns are also limited to their owner (because weapon upgrades are on a per-person basis).