When you take out a mortgage, you allow a lender to place a lien on your home. The lender can sell your home to settle the debt if you fail to repay the mortgage. Generally, yes: both owners are required to sign mortgage documents, although the details and local laws vary.
Mortgage
A mortgage document is a legally binding contract that your lender files at the local county courthouse as evidence that you have borrowed money against your home. A lender can't place a mortgage unless all of the property owners consent to the lien being placed.This is why both owners must sign -- both must agree to the lien. The precise wording on mortgage agreements varies among states, but as an owner you must either consent to the lien or at least acknowledge the fact that the lender has a right to place the lien.
The Note
A mortgage document contains a loan agreement called a note. The fact that you signed the mortgage as an owner doesn't necessarily mean that you also have to sign the note. If your spouse has bad credit, it might make more sense for you to take out the loan in your name alone, qualifying on the basis of your income and credit score. Your spouse has no obligation to repay the loan, and therefore doesn't need to sign the note, but he must still sign the mortgage document as an owner consenting to the lien.
Community Property States
In states with community property laws, your spouse is normally entitled to an ownership stake in your primary residence -- although this isn't always the case with real estate that you bought before you got married. If your spouse does have a legal claim on the home, he or she may have to sign the mortgage documents as an owner, even if her name does not appear on the deed.
Other State Laws
In some states, such as Minnesota and Wisconsin, you can buy a primary residence without involving your spouse and if you do, your spouse doesn't have to sign the mortgage documents. In cases like this, your spouse does have certain ownership rights to the home but these rights can't stop a lender from foreclosing on the home if you fail to repay the mortgage.
Rules in many states are different for rental and vacation homes as opposed to your primary residence. In states such as Florida, one spouse can own and finance a rental home without involving the other but both spouses must sign a mortgage for a primary residence. Under federal tax laws, you can own a home bought with inherited funds in your name alone without involving your spouse but state laws on inheritance rules vary.