script.aculo.us is a JavaScript library built on the Prototype JavaScript Framework, providing dynamic visual effects and user interface elements via the Document Object Model.

It is most notably included with Seaside and Ruby on Rails, but also provided separately to work with other web application frameworks and scripting languages.

script.aculo.us was extracted by Thomas Fuchs from his work on fluxiom, a web based digital asset management tool by the design company wollzelle.[1] It was first released to the public in June 2005.