Tech levels 0 - 4.

Despite being designated as Technology Zero, this tech level represents probably the widest range of technological achievements on the entire scale - from chimpanzees bashing rocks together, to complex agriculture, cities and social civilisations. It also represents no technology at all - a barren world completely devoid of life is also defined as TL 0, though in practise there is considered a difference between no technology and TL 0.

The principle defining characteristic of a TL 0 society is that it has not figured out how to process metals. There is a difference between processing and using metals. Gold is often discovered quite early, and used as jewellery or a form of currency, but actually refining and processing metals is considered the domain of TL 1 and above.