It occurs to me that not everyone might know what Ranma ½ is. Ranma is a Japanese Manga/Anime. It was created by Rumiko Takahashi. The manga ran from 1987-1996 in Japan. It is 38 volumes long (Viz version 36 volumes). Television had 161 episodes, 11 Oav's (now 12), and 3 movies, several video games, Cds, Music Videos, and a card game (also figurines, posters, shirts, action figures, blankets, phone cards, etc.) More than 49 million copies of the manga were sold in Japan according to a press release made by VIZ on November 6, 2006. Has been/is being officially translated in 19 languages (according to the Japanese Wikipedia) and even more languages unofficially.
The series starts with Ranma (a teenage superhuman martial artist) coming back to Japan from a training journey in China. While in China Ranma fell into Jusenkyo. Jusenkyo is a place where many cursed springs exist, anyone who falls into one takes on a curse. Ranma's curse is to turn in to a girl (picture is of Ranma in both male and female form). So now every time Ranma gets hit with cold water he turns into a girl and hot water turns him back to his natural form.
That is not all of Ranma's problems. His father had arranged him to marry a Tendo and never bothered to inform Ranma of that. Ranma eventually finds out that he has another fiancee and a lot of relationship problems. (Guys wanting his girl form, an Amazon "wife", etc.). While this is a romantic comedy there is also a lot of action as well as an underlining darkness to the entire manga.
Ok I admit it that wasn't the greatest of summaries and I probably could write one that is better than that. The reason I don't is that there are plenty of pretty good summaries elsewhere on the internet, Furinkan.com, for example has a pretty good summary. Though really I think everyone should just read the manga and read it at least twice. It is not difficult to get and can be purchased from here. It can be downloaded using bittorrent (just use one of the torrent searches). It can even be read on-line in various places.