Birth records are the single most important document that a genealogist can aquire. These are some of the items which can often be found in the birth document (USA). See links at bottom for Overseas Info.
Full name at birth
Date of Birth
Place of Birth
Name of Father
Name of Mother (Sometimes with Maiden Name)
Name of Hospital
Name of Delivery Doctor
The last two (hospital and Doctor)are usually not found until after 1920 (depending on wether the person was born in Urban or Rural Area). Birth certificates are a primary source for the obvious reasons but also because they are usually acurate. Most states required a filing of a birth certificate after 1911. But most vital statistic offices did not exist until later and birth certificates were kept at county courthouses. Fires, floods and the Civil War may have destroyed the courthouse at one time. I know that my grandmother's birth certificate was destroyed by fire and when she was applying to Social Security she had to get a school census record to prove her age. The School Census had her age off by one year.
LOOKING FOR RECORDS PRIOR TO 1911
When looking for birth records before 1911 you most likely will have to write the State Archives of the State the person was born in.
You will have to at least their birth year and county/city to be searched. Sometimes they ask for the name of parents if it is known. Most archives require you to fill out a form to perform the research and will mail and tell you if the person is listed or not listed on the microfilm archive. If the person is listed they will provide you with the info to get a copy of the record. If the person is not listed it could very well mean that a record was never made of the birth or the person was not born in the state. If this is the case there are many other documents that can give you a record of birthdate/birthplace. Census records for 1900 listed Month and Year of birth. See our section Census Records for more detail.