Growing up with both biological parents isn't always a given, so it's not uncommon to know little about your biological father when you reach adulthood. There are as many reasons for wanting to change that as there are parents and children, and you may well wonder how to find your biological father. There are many resources available to help you find your dad for free online, if you're prepared to put in the work.

Your search will be much easier if you know your biological father's name. If you were raised by your biological mother, start by asking her. If she will not cooperate, ask other family members or her friends for help. His name may be on your birth certificate. However, if you were adopted, you probably need to try to obtain your original birth certificate, which should have at least your birth mother's name and may have your birth father's name as well. Some states, such as Alaska, Alabama, Oregon, Kansas, Maine, New Hampshire, and Rhode Island, allow birth certificates to be easily accessed by adult adoptees. Other states make birth certificates accessible to adoptees born before or after a certain year, while still others require a court order. Check the laws of your state. With that vital piece of information in hand, you can move on to the actual research stage.

Search social networking websites. Once you know your father's name, you can search for him on social networking sites. Many people use these sites to connect so your chances are high that you can find him there. Knowing the possible location of your father and other information can help you narrow down your search.

Use websites geared towards finding people online. Sites such as intellius.com, zabasearch.com and pipl.com can dig up anything from email addresses to physical addresses and phone numbers. Search using your father's name and, if possible, his location.

Enter your father's name into an online phone book. An online phone book can show you where your biological father may be living. However, it can be difficult to weed through the results, especially if your father has a common name.

Sign up with a reunion registry. Sometimes the person you are looking for may also be looking for you. You can do this even if you don't know your father's name. The International Soundex Reunion Registry is one of the most commonly used registries for adoption situations. Register with your information so that you can find your biological father if he is also looking for you. Some localities also have their own reunion registries. If there is one for your area, sign up for that one as well. ISRR has the advantage of accepting registrants from anywhere in the world, at no cost. You can also register if you were separated from your father by foster care or divorce.