 <p>For what you want this is not the best way of doing it. However what you're talking about requires knowledge of one of the fundamental tennets of PHP and programming in general aka scope, namely what the global scope is.</p> <p>So, if you declare this in the global scope:</p> <pre><code> $uom = new UOM_Class(); </code></pre> <p>Then in any file afterwards you write:</p> <pre><code>global $uom; $uom-&gt;something(); </code></pre> <p>it will work.</p> <p>This is all wasteful however, instead you would be better with static methods, and something more like a singleton pattern e.g.:</p> <pre><code>UOM::Something(); </code></pre> <p>I leave it as a task for you to learn what a singleton is, and what scope is, these are fundamental tennets of PHP, and you should not claim to know PHP without knowing about scope. The best way of putting it is when in everyday conversation, it is called <em>context</em>, the global scope is tantamount to shouting in everyones ear at the same time. Everyone can access it, and its not something you want to pollute</p> <p>I'm sorry if I seem a bit harsh, here's some articles that should help, they talk about scope, singletons and some other methods of doing it, like object factories</p> <p><a href="http://php.net/manual/en/language.variables.scope.php" rel="nofollow">http://php.net/manual/en/language.variables.scope.php</a> http://www.homeandlearn.co.uk/php/php8p2.html</p> <p><a href="http://php.net/manual/en/language.oop5.patterns.php" rel="nofollow">http://php.net/manual/en/language.oop5.patterns.php</a></p>