 <p>As many as you want. After one commits the file and a second updates the changes the file gets merged. If the first user altered something that the second also altered, the update will result in a conflict and the user will have see what's different from the local file to the one the first user altered and has to manually choose how the file should end up <a href="http://tortoisesvn.net/docs/release/TortoiseSVN_en/tsvn-dug-conflicts.html" rel="nofollow">see solving conflicts in tortoise</a>.</p> <p>If the users modify different parts of the file then there's no issue to it and the file is merged on update.</p>