How to: Redirect in PHP

Summary of existing answers plus my own two cents:

1. Basic answer

You can use the header() function to send a new HTTP header, but this must be sent to the browser before any HTML or text (so before the <!DOCTYPE ...> declaration, for example).

header('Location: '.$newURL);

2. Important details

die()

header("Location: http://mydomain.com/myOtherPage.php");
die();

Why you should use die(): The Daily WTF

Absolute URL

The URL must be an absolute. See RFC 2616. But in most cases a relative URL will be accepted too.

Status Codes

PHP's "Location"-header still uses the HTTP 302-redirect code, but this is not the one you should use. You should consider either 301 (permanent redirect) or 303 (other).

Note: W3C mentions that the 303-header is incompatible with "many pre-HTTP/1.1 user agents. Currently used browsers are all HTTP/1.1 user agents. This is not true for many other user agents like spiders and robots.

3. Documentation

HTTP Headers and the header() function in PHP

What the PHP manual says
What Wikipedia says
What the W3C says

4. Alternatives

You may use the alternative method of http_redirect($url); which needs the PECL package pecl to be installed.

5. Helper Functions

This function doesn't incorporate the 303 status code:

function Redirect($url, $permanent = false)
{
    header('Location: ' . $url, true, $permanent ? 301 : 302);

    exit();
}

Redirect('http://www.google.com/', false);

This is more flexible:

function redirect($url, $statusCode = 303)
{
   header('Location: ' . $url, true, $statusCode);
   die();
}

6. Workaround

As mentioned header() redirects only work before anything is written out. They usually fail if invoked inmidst HTML output. Then you might use a HTML header workaround (not very professional!) like:

 <meta http-equiv="Location" content="http://example.com/">

Or a Javascript redirect even.