The black-and-white process is based on the same chemical concepts (silver halides, developer, fixer) that Daguerre used in 1839. Of course, it's a lot less messy these days - for a long time they had to coat either copper or glass with stuff and take the photo before it dried - and the chemicals are more refined, but it's basically the same process. The developer I use - Rodinal - was patented in the 19th century!

Colour is a whole different ballgame, though. The current negative process is called C41, and only dates to 1972.