How can I make a field conditional based on the entry of another field?

http://form.jotformpro.com/form/41906096369969

I have a simple entry form for a postal catalog. We have a seperate opt-in email address list that we would like to people to join on the same form. We are very concerned with privacy and definitely want every person that subscribes to "opt-in" by checking "Yes" (see form URL above). 

I would like to create a scenario where the email address field is not available for data entry unless the "Yes" radial button is checked. Is this possible and how do I do it?

It is possible.

You can add a condition to show the email field if the user says yes to that question:

You can test and clone the form if you wish:

http://form.jotformpro.com/form/41974650174964?

If you need further support please let us know, as we're here to help.

Thank you thank you!