How can I get a user to choose in which group he registers using the User Registration Form Is there a way to allow a registrant to choose a user group in the registration form?

I tried using the following code but it didn't work:

&lt;input type="hidden" name="userGroups" value="3"&gt;
As far as I know there is no way to do this without a plugin. However, developing a plugin for this is not difficult. In your form you would want to add an additional drop-down, multi-select, or checkbox field with your groups listed. Then in your plugin, create a listener in your plugin's init method that listens for the users.saveUser event, and dynamically assigns the user to the selected groups based on the user's selection. For an example see this post explaining how to respond to an onSaveUser event, and this post on assigning groups dynamically.