Email marketing is one of the most reliable tools a marketer has in his repertoire. But it’s of no use without an email list to market to.

Online businesses build these email lists with opt-in forms: A form placed on your website to collect email addresses. However, not all opt-in forms are created equal.

A great design will build your email list bottom-up while a poor one will only sit collecting dust.

So, what makes an opt-in form great?