The Henry system is a well-known genealogical numbering system. This system assigns a particular number to the progenitor, or the ancestor farthest back (that you know about) in your family line. Then each of the progenitor's children is assigned a number in a sequence that starts with his number and adds the numbers 1, 2, 3, and so forth through 9.

If the progenitor had more than nine children, the tenth child is assigned an X, the eleventh an A, the twelfth a B, and so on. Then the children's children are assigned the parent's number plus a number in sequence (again 1 through 9, then X, A, B, and so on).

For example, if progenitor number one (1) had 12 children, his children would be 11, 12, 13,…1X, 1A, and 1B. The eleventh child's children would be assigned the numbers 1A1, 1A2, 1A3, and so on.

For example, suppose that one of your ancestors, John Jones, had 12 children. The names of these children were Joseph, Ann, Mary, Jacob, Arthur, Charles, James, Maria, Esther, Harriett, Thomas, and Sophia. Joseph had one child named Gertrude, and Thomas had three children named Lawrence, Joshua, and David. Under the standard Henry system, the children's children are numbered like this:

1    John Jones
11    Joseph Jones
111    Gertrude Jones
12    Ann Jones
13    Mary Jones
14    Jacob Jones
15    Arthur Jones
16    Charles Jones
17    James Jones
18    Maria Jones
19    Esther Jones
1X    Harriett Jones
1A    Thomas Jones
1A1    Lawrence Jones
1A2    Joshua Jones
1A3    David Jones
1B    Sophia Jones

Ahnentafel and Henry are just two of the easier systems to learn. Several others have been designed to display genealogies in book form, such as the Register system (based on the style of the New England Historical and Genealogical Register) and the National Genealogical Society Quarterly system.

If you're curious about some of these systems, take a look at the Numbering Systems in Genealogy page. There you can find descriptions of each major numbering system and variations of these systems.

If you decide to use a numbering system, you can place the corresponding unique number for each individual in the file that you set up for that person in your paper record-keeping system, as well as in your genealogical software.