R Markdown supports many other languages besides R through a variety of language engines implemented in the knitr package. This chapter first explores how custom language engines are implemented with knitr to provide a blueprint for you to develop your own. The remainder of the chapter provides an overview of the broad range of currently-implemented language engines. Options include prominent programming languages such as python, bash, D3, CSS/Sass, SAS, and Stata as well as utility engines such as asis (for verbatim content), cat (for writing contents to a file), and Asymptote (for advanced vector graphics).