Tenchi Muyo is the story of a boy named Tenchi Misaki, and all of the events that happen around and to him.  Originally it started as a composite of the best attributes of some of the various Anime, but soon took on a life of it's own.  It spans many different genres.  It has a complex Science Fiction plot, a nice romantic comedy element (a classic Guy surrounded by Girls match), a bit of fantasy, especially in the first episode, and many times, a sit-com-ish look at life.  Currently there are 2 OAV series for Tenchi Muyo (with rumors of a third) and 1 TV series and three movies.  In addition, there is also a Manga (or Comic book) that was done in Japan, and is distributed in America under the title: "No need for Tenchi". Likewise there is a new Comic book, being done in America under the title of "Tenchi Muyo".  Originally Tenchi Muyo was a concept pitched to Pioneer.  Pioneer contracted AIC, an Anime production studio to do 6 OAV's.  An OAV is an animation that is released strait to video, and is not shown on TV or in a movie.  Later, Pioneer did 7 more OAV's.  The Tenchi OAV's are much more complex than the TV series.  The initial story revolves around introducing the characters.  The first series in general establishes the love triangle of Tenchi, Ayeka, and Ryoko.  The villain in the first series is Kagato.  There is also a second OAV series, but the second series, in the eyes of many fans, does not live up to the first series.  There are 13 OAV episodes currently.  The Tenchi TV series has the same characters as the OAV's, but the plot is drummed down, to reach a younger age demographic.  The story line is completely different.  The Tenchi Movie, Tenchi Muyo in Love, is based on the TV series, but tends to be fairly story line independent.  There are also some novels that have not been brought over.