Prepared by Elisabeth Lindsay.
In genealogy the term direct line refers to a relationship of one person to another in a direct line. A direct-line ancestor is someone from whom you descend in a direct line, parent to child, grandparent, great-grandparent, etc. Direct-line research refers to genealogy research focused on one's direct-line ancestors. By contrast, collateral line is a term used to describe family relationships not in the direct line of descent such as siblings, spouses and children of siblings, aunts, uncles, cousins, etc.
Researching direct-line ancestry is a common focus of genealogists and family history researchers. Proving a direct line of descent is generally required for membership in heritage societies. Collateral line research is also important for revealing clues to direct-line ancestors.