mod_expires in apache

This module controls the setting of the Expires HTTP header and the max-age directive of the Cache-Control HTTP header in server responses. The expiration date can set to be relative to either the time the source file was last modified, or to the time of the client access.
These HTTP headers are an instruction to the client about the document's validity and persistence. If cached, the document may be fetched from the cache rather than from the source until this time has passed. After that, the cache copy is considered "expired" and invalid, and a new copy must be obtained from the source.

Sample Configuration:

<IfModule mod_expires.c>
 ExpiresActive On
 ExpiresByType image/jpg "access plus 60 days"
 ExpiresByType image/png "access plus 60 days"
 ExpiresByType image/gif "access plus 60 days"
 ExpiresByType image/jpeg "access plus 60 days"
 ExpiresByType text/css "modification plus 10 days"
 ExpiresByType image/x-icon "access plus 10 month"
 ExpiresByType application/pdf "access plus 1 month"
 ExpiresByType audio/x-wav "access plus 1 month"
 ExpiresByType audio/mpeg "access plus 1 month"
 ExpiresByType video/mpeg "access plus 1 month"
 ExpiresByType video/mp4 "access plus 1 month"
 ExpiresByType video/quicktime "access plus 1 month"
 ExpiresByType video/x-ms-wmv "access plus 1 month"
 ExpiresByType application/x-shockwave-flash "access 1 month"
 ExpiresByType text/javascript "access plus 1 week"
 ExpiresByType application/x-javascript "access plus 1 week"
 ExpiresByType application/javascript "access plus 1 week"
</IfModule>