First, we should look at what the scope of the discharge is. All debts that were incurred before the bankruptcy or were perceived to have been incurred prior to bankruptcy are subject to discharge. It does not matter that a pre-petition creditor did not receive any distribution from your estate, their debt will still count to discharge.
Of course, there are exclusions from discharge by statute. And remember, only individuals can receive a discharge in Chapters 7 and 13. (Corporate entities may receive a discharge in Chapters 11 and 12, but for the purposes of this discussion, we are not talking about those particular cases). Corporations in Chapter 7 are dissolved upon the conclusion of their case, and do not receive a formal discharge.
Now, the most common issue that arises with my clients is tax debt. What tax debt is dischargeable, and what tax debt sticks with you after your bankruptcy concludes? Well, federal taxes can be discharged if they were filed more than three years before you filed bankruptcy, irrespective of the tax year. State taxes vary from state to state, but the general rule in New Jersey is two years from the date of filing. So, you cannot claim that your 2011 taxes ought to be discharged in a bankruptcy filed in 2015, when you didn't even file those taxes until 2014!
On a related note, if you didn't even file the return at all, those debts are not subject to discharge. As you can expect, fraudulent returns are not subject to discharge as well, but if you commit tax fraud, being ineligible to have those debts discharged in bankruptcy is probably the least of your worries.
Another issue which is frequently litigated relates to debts based on fraud. To put it simply, if you incurred a debt by fraudulent means, you can't get rid of that debt in bankruptcy. This is accomplished by filing a complaint objecting to discharge, more commonly known as an "adversary proceeding," which is an uphill battle for the plaintiff and a source of ulcers for the debtor's attorney.
If you forget to include a debt in your bankruptcy petition, that debt may not be dischargeable. Courts are split on how this applies to a "no-asset" case, where there are not assets to distribute to creditors, but regardless, it is important to make sure all debts are included in your petition, even if you aren't sure how much you owe, or even if you don't think you owe anything. Notice is the important factor in bankruptcy.
Domestic support obligations cannot be discharged in bankruptcy, and often may lead to other issues once the former spouse becomes aware of the bankruptcy filing.
Another big class of debts is student loans. Those are almost always not subject to discharge. Now, there is an exception, which was outlined in Brunner v. N.Y. State Higher Educ. Servs. Corp. out of the Southern District of New York in 1985. Basically, you would be required to show that you cannot maintain a minimal standard of living for you and your family if you are forced to repay the loans, and that you have made a good faith effort to repay the loans. Even then, this is not a guarantee that your loans will be discharged. So if you are interested in bankruptcy for the sole purpose of getting rid of your student loan debt, this may surprise you.
There are a handful of other exceptions, but the ones listed above are the most common that I see in my practice. The remaining debts, your credit cards, medical bills, mortgages, car loans -- all can be discharged. Note that in the case of a secured debt, your personal obligation to pay the debt is extinguished, but the lien on the collateral remains, and the lender may assert their rights in the collateral post-discharge. If you intend to keep a house or a car, you may have to reaffirm the debt or work out some other arrangement with the lender to continue monthly payments.