Also, "The Evolution of Lua" — an interesting paper that shows how they came to this fast and somewhat elegant language: http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.72.... [PDF]
Past discussion: http://news.ycombinator.com/item?id=617278
If you want to learn Lua, Ierusalimschy's _Programming in Lua_ (http://www.inf.puc-rio.br/~roberto/pil2/) is by far the best book. Lua is one of my favorite languages. While it's good on its own, you'll get a lot more out of it if you're comfortable with C. Lua+C is an excellent combination.
Lua Performance Tips: (http://www.lua.org/gems/sample.pdf)
A No-Frills Introduction to Lua 5.1 VM Instructions: (http://luaforge.net/docman/view.php/83/98/ANoFrillsIntroToLu...)