Records and careful documentation becomes the foundation of genealogical research. Any historical document written during the life time of the person under research is called a "Primary Document". Deeds, wills, court orders and records, birth certificates, death certificates, census data, military records, and many other items woven into a coherent thread produces a record of the family tree. For me, my favorite primary docuement is shown:
It is a Revolutionary War Pension application from my sixth generation grandfather Nicholas Jones. It contains his actual signiture [shown] and additional family information. What a deal for me! A grandfather giving his hand over generations, reaching me thorough the ages. A family treasure it is.
What is your own favorite primary document?