The official definition of the Lua language is its reference manual, which describes the syntax and the semantics of Lua, the standard libraries, and the C API.
For a detailed introduction to the practice of Lua programming, see the book Programming in Lua, also available as an e-book.
The manual for the latest version of Lua is available in English only:
The manual for Lua 5.2 is available in English and in Portuguese:
The manual for Lua 5.1 is available in several languages:
Buy a copy of this book and help to support the Lua project.
The manuals for older versions are available in English only:
These manuals are also available here in PostScript and PDF.
All reference manuals are freely available under the terms of the Lua license.