utf8_encode

Please note that utf8_encode only converts a string encoded in ISO-8859-1 to UTF-8. A more appropriate name for it would be "iso88591_to_utf8". If your text is not encoded in  ISO-8859-1, you do not need this function. If your text is already in UTF-8, you do not need this function. In fact, applying this function to text that is not encoded in ISO-8859-1 will most likely simply garble that text.

If you need to convert text from any encoding to any other encoding, look at iconv() instead.

Here's some code that addresses the issue that Steven describes in the previous comment; 

<?php

/* This structure encodes the difference between ISO-8859-1 and Windows-1252,
   as a map from the UTF-8 encoding of some ISO-8859-1 control characters to
   the UTF-8 encoding of the non-control characters that Windows-1252 places
   at the equivalent code points. */

$cp1252_map = array(
    "\xc2\x80" => "\xe2\x82\xac", /* EURO SIGN */
    "\xc2\x82" => "\xe2\x80\x9a", /* SINGLE LOW-9 QUOTATION MARK */
    "\xc2\x83" => "\xc6\x92",     /* LATIN SMALL LETTER F WITH HOOK */
    "\xc2\x84" => "\xe2\x80\x9e", /* DOUBLE LOW-9 QUOTATION MARK */
    "\xc2\x85" => "\xe2\x80\xa6", /* HORIZONTAL ELLIPSIS */
    "\xc2\x86" => "\xe2\x80\xa0", /* DAGGER */
    "\xc2\x87" => "\xe2\x80\xa1", /* DOUBLE DAGGER */
    "\xc2\x88" => "\xcb\x86",     /* MODIFIER LETTER CIRCUMFLEX ACCENT */
    "\xc2\x89" => "\xe2\x80\xb0", /* PER MILLE SIGN */
    "\xc2\x8a" => "\xc5\xa0",     /* LATIN CAPITAL LETTER S WITH CARON */
    "\xc2\x8b" => "\xe2\x80\xb9", /* SINGLE LEFT-POINTING ANGLE QUOTATION */
    "\xc2\x8c" => "\xc5\x92",     /* LATIN CAPITAL LIGATURE OE */
    "\xc2\x8e" => "\xc5\xbd",     /* LATIN CAPITAL LETTER Z WITH CARON */
    "\xc2\x91" => "\xe2\x80\x98", /* LEFT SINGLE QUOTATION MARK */
    "\xc2\x92" => "\xe2\x80\x99", /* RIGHT SINGLE QUOTATION MARK */
    "\xc2\x93" => "\xe2\x80\x9c", /* LEFT DOUBLE QUOTATION MARK */
    "\xc2\x94" => "\xe2\x80\x9d", /* RIGHT DOUBLE QUOTATION MARK */
    "\xc2\x95" => "\xe2\x80\xa2", /* BULLET */
    "\xc2\x96" => "\xe2\x80\x93", /* EN DASH */
    "\xc2\x97" => "\xe2\x80\x94", /* EM DASH */

    "\xc2\x98" => "\xcb\x9c",     /* SMALL TILDE */
    "\xc2\x99" => "\xe2\x84\xa2", /* TRADE MARK SIGN */
    "\xc2\x9a" => "\xc5\xa1",     /* LATIN SMALL LETTER S WITH CARON */
    "\xc2\x9b" => "\xe2\x80\xba", /* SINGLE RIGHT-POINTING ANGLE QUOTATION*/
    "\xc2\x9c" => "\xc5\x93",     /* LATIN SMALL LIGATURE OE */
    "\xc2\x9e" => "\xc5\xbe",     /* LATIN SMALL LETTER Z WITH CARON */
    "\xc2\x9f" => "\xc5\xb8"      /* LATIN CAPITAL LETTER Y WITH DIAERESIS*/
);

function cp1252_to_utf8($str) {
        global $cp1252_map; 
        return  strtr(utf8_encode($str), $cp1252_map);
}

?>

If you haven't guessed already: If the UTF-8 character has no representation in the ISO-8859-1 codepage, a ? will be returned. You might want to wrap a function around this to make sure you aren't saving a bunch of ???? into your database.