The Soundex is a code developed in order to remove the different phonetic pronunciations of surnames and to get them standardized. Up until the 20th century, surnames were not spelled the same way every time as a rule. Soundex is a code that is used by many depositories like NARA to sort surnames. You need this code to find names on census records and passenger lists. Simply put your soundex code for your surname starts with the first letter of your name followed by a 3 digit number. For example ALTMAN would be A-435. Jones would be J-520. Gilbert would be G-416. To find your soundex code, you can go to an online soundex converter like the one found at http://www.rootsweb.com.

Or you can convert it yourself. It's fairly easy. Keep the first letter of your surname (if you have a surname like de Villeroi you can use either D or V, it would be prudent to check for both). Then cross out all of the vowels (A, E, I, O, U, and also H, W, Y). Then you assign numbers to the remaining letters as follows:
** If the letter is B, F, P, or V then you assign it the number 1.
** If the letter is C, G, J, K, Q, S, X, or Z assign it the number 2.
** If the letter is D or T then it is assigned the number 3.
** If the letter is L assign it the number 4.
** If the letter is M or N assign it the number 5.
** If the letter is R assign it the number 6.

Assign these numbers in order. Do not assign numbers to repeating letters. For a surname like Petterson, the double "T's" would only be counted as a single letter. Only go up to 3 numbers, no more. If you have less than 3 numbers just add zeros until you have 3. Not every repository uses the exact same soundex rules. For a really good article on soundex and how the name ASHCROFT is coded in 2 different ways read Tony Burroughs article on the soundex system in the National Genealogical Society's Journal. You can contact them at http://www.ngsgenealogy.org for back issues.