Readmore not working

A Readmore tag has been added to the article but is not showing in the front-end.

The Readmore option must be enabled in the Article Manager Options

Joomla! 1.5

1. In the Article Manager, click on the Parameters button
2. Set the Read More...Link option to Show
   
    

Joomla! 1.7

1. In the Article Manager, click on the Options button.
2. Set the Show "Read More" option to Yes
   
    

A readmore will only appear in a blog layout

As listed in the Joomla! Documentation - Splitting an Article into an introduction with a link to read more :

The "read more" function works only in articles published in blog layout.