Do All WordPress Themes Allow Plugins?

Administrative Plugins

The most common plugins are administrative. These expand the options available to the WordPress administrator, and include changes like integrating Google AdSense, optimizing the blog for search engines and tracking visitor statistics. Administrative plugins rarely require template integration. Typically, any interaction they have with the front-end of the website is handled entirely by the code.

Front-End Plugins

Front-end plugins alter the way the site is displayed to visitors or add extra options for display. For example, a front-end plugin can integrate a new JavaScript file to display a special image gallery or allow the user to switch theme colors or styles. This type of plugin may require template modification, but it is generally compatible with all themes.

Widgets

A WordPress widget is a plugin that displays a block of content. Widgets are selected and placed in the administrative menu and display on the front-end to the visitor. By default, WordPress includes widgets to display all categories, recent posts and comments, and a block of text, among others. Themes must be widget-ready or 'widgetized' to handle these plugins properly. Most new themes are widgetized by default, but older themes may need modification.

Functions

Although not truly a plugin, the functions.php theme file can house modifications that act as plugins. Since this file is typically coded at the same time as the theme by the developer, modification is rarely needed. However, if you add extra functionality for your theme in this file, you may need to edit other files to reflect the changes.