Those who wish to play some multiplayer in The Master Chief Collection are unfortunately not able to due to various server problems. Microsoft is aware and has issued an update.
The game's matchmaking system currently appears to be broken, with players unable to find a multiplayer game or be partied up with other users.
"As you read this message, we're working with our external partner to correct this issue right away," Microsoft said on its support site. "We appreciate your patience in the meantime!"
Xbox Live currently appears to be suffering from an issue preventing some users from viewing their Friends list, too.
"Additionally, it's come to our attention that some of our members are unable to view the online state and activity of other users on their Friends list," added Microsoft. "Don't worry folks, we're on it! Thanks for hanging in there while we work. We'll provide an update for you as soon as possible."
Microsoft has yet to provide an ETA on a fix for Halo's matchmaking.