It's not uncommon for there to be more than one investment account holder in one household. If multiple members of your household are shareholders of the same company, your residence might get two or more mailings of the same information: companies directly send out information to each individual shareholder. Given the size and the amount of documents that companies send, it's easy to see why you wouldn't want a company to send more than one copy to your house.
Aware of this problem, the SEC has created "householding rules" that permit investors who are considered of the same family to be omitted from duplicate mailings. This omission occurs by the investors' implied consent, whereby investment companies can assume that only one document per household is sufficient. The documents to which the householding rules apply are the single prospectus, annual and semi-annual reports, and proxy and information statements.
It is up to the discretion of each individual company to decide initially whether to apply householding rules, so you may still get duplicate mailings even if you don't want them. You can, however, request that your household receive only one copy of each mailing. Conversely, if you want duplicates but they aren't coming to you, you can ask for them. You can make either of these requests by simply calling the company's investors' information line.
To read more on this subject, see Knowing Your Rights As A Shareholder.