The Fair Debt Collection Practices Act (FDCPA) is a federal law that was put in place to protect you against the abusive and/or unethical collection tactics sometimes employed by debt collectors. At the federal level, the FDCPA applies only to third-party collection agencies and junk debt buyers; however some states do have laws that also govern the debt collection practices of original creditors. Some states also provide consumers more rights against debt collectors in addition to those already included in the federal version of the FDCPA.

I have summarized the FDCPA in plain English below, but if you would like to read the law in its entirety, you can do so here.
Here is what debt collectors may not do according to the FDCPA:

-call you before 8 AM or after 9 PM
-call you at work after you have advised them that such calls are inconvenient for you and/or are forbidden by your employer
-communicate with third parties about your debt if they already have your current contact information on file. In the event that a debt collector does not have your current address or phone number, they may contact a third party to locate you only. They may not disclose any information to that third party regarding your alleged debt; in fact, they are not even allowed to mention the debt at all. They also may not contact anyone else on more than one occasion about your debt; they can call once to locate you and that’s it.
-misrepresent or refuse to disclose their identity
-attempt to communicate with you directly if they are aware that you’re being represented by an attorney
-misrepresent the nature of the debt
-use profanity, call you names, or otherwise verbally abuse you
-make threats that they cannot or do not intend to follow through on (for example: threatening to sue you if they have no intention of doing so, or threatening to have you arrested and thrown in ‘debtor’s jail’–and no, there is no such thing!)
-continue collection activity without properly validating the debt after you have requested validation
-continue collection activity after you have instructed them to cease and desist communication with you (although at that point they may file suit against you in an effort to recover the debt, provided the debt is within the statute of limitations)
Despite the fact that severe penalties may be imposed on debt collectors who violate the FDCPA (for example, they are liable to you for $1000 per incident!), there are some collectors who continue to disregard this law. And sadly, they often get away with it simply because so many consumers are not aware of their rights.

These companies harass, intimidate, and deceive their victims into submission, and this might very well be the only reason a lot of them stay in business. It is my goal to put a big dent in these unscrupulous, law-breaking debt collectors’ profits by arming each of you with knowledge of the rights afforded to you by the Fair Debt Collection Practices Act (FDCPA)!