How many people can play multiplayer factorio together?

The hard limit is currently 255. We never tested it for more than 12 people on local network so different kind of problems might arise when lot of people play.

Edit: Since 0.14 the limit has been increased to 65535 and it might actually be possible to get that number of players online with exceptionally good network connection.

The hard limit for number of players playing together is 65535.

Because it is in early access, some content may be buggy, so we cannot say for sure exactly how many players will be able to play together (this should also increase over time).