CiviCRM Community Forums (archive)

I don't think you can have a form just for membership renewals, but we fake this with a form that's only accessible from members' areas - so the only people can access it must be members already. People could theoretically get to it if they knew the link, though, but you could probably add some code to detect non-members accessing the page.

Although Civi will match on email addresses, afaik you can't renew without being logged in (not sure how Civi would tell whether someone wants a new membership or to renew an old one) - but someone may correct me on that. But, you can email a link with a checksum that automatically fills in the person's details. So if the member clicks that they can renew without logging in.

Here is a snippit from one of the email message template that might help:
We sincerely hope that you will take the next five minutes to renew your membership: http://<our website>/civicrm/contribute/transact?reset=1&amp;id=9&amp;{contact.checksum}&amp;cid={contact.contact_id}.