A template processor (also known as a template engine, template parser or template language) is software or a software component that is designed to combine one or more templates with a data model to produce one or more result documents. For purposes of this article, a result document is any kind of formatted output, including documents, web pages, or source code, either in whole or in fragments.

All template processing systems consist of at least these primary elements:

This may be a relational database, a source file such as XML, an alternate format of flat file database, a spreadsheet or any of other various sources of preformatted data. Some template processing systems are limited in the types of data that can be used. Others are designed for maximum flexibility and allow many different types of data.

Source templates are traditionally specified:

The template engine is responsible for:

Additionally some template engines allow additional configuration options.

These may consist of an entire document or a document fragment.