In English, one letter can represent more than one sound, and one sound can be represented by more than one letter. Thus two names (surnames or place names) that are pronounced exactly the same can be spelled in very different ways. For that reason, Robert C. Russell developed the American Soundex System, dividing each consonant in the English language into eight categories:

1. Sounds made with lips (b, f, p, v)
2. Gutturals and sibilants (c, g, k, q, s, x, z)
3. Sounds made with the tongue and teeth, or the tongue and the roof of the mouth (d, t)
4. l, a unique sound
5. m and n
6. r, a unique sound

Under the American Soundex System, many Eastern European Jewish names that sounded the same did not have the same Soundex code. The letters w and v were problematic, since they should have been interchangeable for the sake of Jewish names (like the surnames Moskovitz and Moskowitz, for instance).

In the first issue of the AVOTAYNU genealogy newsletter, Gary Mokotoff published an article entitled, "Proposal for a Jewish Soundex Code." One major difference between this system and the American Soundex System was that in this system the first letter of a name was encoded as a number. If the first letter was a vowel, it was assigned as a zero. Double-letter combinations that essentially represented the same sound (such as tx, tz, and tc) were coded with a single number. (see Footnote Below)

Randy Daitch, another researcher of Jewish genealogy, responded to Mokotoff's article by proposing the following additional changes:

• Names would be encoded to six places, or six digits, rather than four. This would give the researcher fewer surnames to check.
• Other multiple-letter combinations from Slavic and German were added.
• For the purpose of databases, if a combination of letters could have two possible sounds, it was encoded in both ways (a hard ch versus a soft ch, for instance).

The new system, with the contributions of Mokotoff and Daitch, became the Daitch-Mokotoff Soundex System. It is sometimes nicknamed the Jewish Soundex System or the Eastern European Soundex System, and it has become standard for all indexing projects conducted by Jewish genealogical organizations.

(Footnote): Gary Mokotoff, "Daitch-Mokotoff Soundex System," Appendix D, Avotaynu Guide to Jewish Genealogy,ed. Sallyann Amdur Sack and Gary Mokotoff (Bergenfield, New Jersey: Avotaynu, 2004), 591-594.