It's a paradox: while buckwheat has been cultivated in Japan since the Jomon era, or fifteenth century, soba noodles are one of the only dishes in which it's used (along with sobagaki, buckwheat dumplings).
They are very rarely made using 100% buckwheat, more often from a mixture of flours. Confusingly, yakisoba (fried noodles) and Okinawa soba (noodle soup) don't contain any soba!
So, how do you make soba?
According to the saying, the best soba is "hiki-tate, uchi-tate, tate-yude" freshly milled, made and cooked.
The most common way to eat soba is zarusoba, served cold and dipped in a sauce that varies according to region (usually salty and seasoned with bonito and seaweed). Soba can also be served hot in a soup, similar to ramen: This is called kake-soba.
According to tradition, soba should be slurped and then swallowed whole, not chewed, but beware of choking!
Soba dishes quickly became standard at major life events: it's customary to eat soba when moving into a new home, and especially to offer hikkoshi-soba to new neighbors. Toshikoshi-soba is enjoyed just before New Year in hope of staying healthy and living a long life: the elongated shape and dense texture of the noodles representing durability and stability.
A very old dish, soba has many local variations. For example, in Uji, famous for its tea, you can eat soba flavored with matcha (green tea powder); in Kyoto it's eaten accompanied by nishin, grilled fish; in Morioka they enjoy it almost as a game, one that involves eating several small bowls of soba (wanko-soba). Some restaurants also serve you a little teapot or a glass containing some of the soba cooking water at the end of the meal: the idea is to pour it into your remaining sauce and then drink it.