Marmalade Boy (MB) was originally a manga by Wataru Yoshizumi, a Japanese woman (this is her pseudonym). It belongs to the genre "shoujo" which  means that was specially designed for girls, in this case, teenagers. It was published in Japan by the magazine Ribon, specialized in the publication of shoujo manga. While its publication, they decided to create an anime, the "animated" version of the manga. Here in Spain it was called "La Familia Crece" (the family grows), a very stupid title for what it is about.

   
Ribon Magazine (February & May '01 issues)

  Afterwards, the manga was published in volumes in Japan by Ribon Mascot Comics. Here in Spain it has been published by Planeta de Agostini, in 8 volumes or 23 comic-books.  There is also a film, which has the same length as an episode, and in Spain it also includes some interviews to the dubbers. It is available for 1000 pts (6€, 5,55$). I recommend it to you if you like Marmalade Boy and you haven't seen it.

There are also two art books: one with pictures from Wataru Yoshizumi and the other with pictures from the anime.

 
Image from the first art book (Spanish edition)

Apart from that there are hundreds of merchandise like medallions, voice memos with the shape of the robot, trading cards, posters, postcards, dolls, etc; but most of them haven't reached Spain or Europe, and some of them are even difficult to get in Japan.