A layout engine is a type of software or computer program that allows web content as well as its formatting information to be displayed graphically on the computer screen.

By reading code written in HTML, XML on image and text files and then consolidating it with the formatting code provided from CSS, XSL, etc. in order to display correctly on a web browser the content as well as the style that the whole web page was designed to look from a visual perspective.

The layout engine only gained some notability when they were made available separately from the web browser where they were first mainly being used for. The most notable of these layout engines are those of the graphical nature. Different web browsers have used different layout engines to enable web content to be displayed on the computer.

Gecko

Gecko is the layout engine that is developed by Mozilla and used for its Firefox web browser. It was designed to support open standards and it is also used by other applications such as Camino, Flock, SeaMonkey and Netscape 9 to display web pages.

Trident

Trident is the layout engine developed for the Internet Explorer developed by Microsoft. It was first introduced on Internet Explorer 4.0 in 1997 and has been steadily updated and still in use by new versions of the popular web browser.

New versions of Trident have been developed to allow significant changes to improve its compliance with accepted web standards as well as to support new technologies.

Presto

Presto is the layout engine developed for use on the Opera web browser. Presto is considered to be dynamic in that web pages or parts of it can be re-rendered in response to updated DOM and script events. The Presto engine is only available for the Opera browser and related products and is not available for the public.

WebKit

WebKit is the layout engine used by Apple's Safari web browser. This layout engine has an open source application network that programmers can use as a foundation to build a web browser. WebKit originally was developed from another layout engine called KHTML which is used on the Konqueror web browser.

WebKit is considered to be a remodified version of the KHTML engine. WebKit has since been further developed by companies such as Google, Nokia and Apple for their own set of web applications.