Wouldn’t it be great if there was a way to query and display data from multiple lists in SharePoint? With a Microsoft Office SharePoint Server site, those things are not only great — they are possible. Links to list items can be displayed, throughout the site collection, in one specific site and all of its sub-sites, in one specific list.
The Content Query Web Part, is a part of the Enterprise Content Management (ECM) functionality in Microsoft Office SharePoint Server. It aggregates and displays list items within a site hierarchy. It allows the ability to query content across a SharePoint site collection and display it as navigation. The web part does not use search. Rather, it uses the native SharePoint Collaboration Application Markup Language, known as CAML, to find content matching the criteria provided.
The biggest advantage to the web part is that displayed results can be radically customized. This allows organizations a great deal of flexibility when using this web part. For example, the web part can be used to query a Site Collection for all announcements across multiple department sites and display them like navigation elements on the home page of an intranet. To do this, insert the Content Query Web Part. This Web Part can be inserted on any Web Part Page, but it can also be added to a page layout from which publishing pages are created. By adding the Content Query Web Part to a page layout, the results of the query can be made to appear on every publishing page that is created from that page layout. Step by step instructions for configuring a CQWP can be found here.
The items that are displayed by the Content Query Web Part always reflect the most current set of items that are retrieved by the query that the page viewer is authorized to see, retaining security. The query is run whenever the page is viewed. If new content is added and it meets the query criteria, it is automatically displayed by the Content Query Web Part.