We plan to give the main ideas of a proof of the birational anabelian conjecture in this talk and the sequel. We will concentrate on an ``absolute by pro-l'' form of the conjecture, which is a sharpening of the published/known results. In characteristic zero we use/rely -- among other things -- on the (very strong) result by Mochizuki on anabelian geometry over the p-adics. In positive characteristic one uses various other techniques. The results are easy to understand. But in order to understand the methods, some decomposition/ramification theory for Krull valuations is necessary in order to get an idea about the machinery (which then reduces the problem to classical facts from/in class field theory, birational geometry, etc.).