Doujinshi (同人誌) are Japanese comic books (manga) drawn by fans rather than by professional artists (see fan fiction). The term is derived from doujin (同人) or a literary group, which was its original means of production, and shi (誌) which means magazine or distribution.
Some are considered fanwork, but many (CLAMP started with doujinshi) are just small-press manga. Usually they draw from popular manga or anime series but can include older titles or even the artists' original characters. Stories usually consist of a parody or just an original story using the characters from the particular anime in question.
Adult oriented stories and drawings seem like they dominate this field of anime art, but many are, in fact, not necessarily adult-oriented, but are made by people who prefer to print their own comics and/or are looking for the so-called 'big break.' Artists and illustrators of doujinshi, either individual or with the backing of a circle can range from amateurs to professional artists. Avid fans of doujinshi art attend a semiannual doujinshi convention called Comiket (Comic Market) held in the summer and winter in Tokyo. Here, all the new doujinshi and even old doujinshi are bought sold and traded by any and everyone. Doujinshi artists are only allowed to print small numbers of books due to copyright laws. This makes a talented artists' or circles' doujinshi a coveted commodity as only the fast or the lucky will be able to get them before they sell out.
There are a few prevalent categories of doujinshi. Seinen doujinshi usually contain adult material and target adult males over 18. Yaoi and shounen-ai doujinshi feature graphic and not so graphic depiction's of male homosexuality and usually target adult women; yuri and shoujo-ai are the lesbian equivalent. Ippan doujinshi do not contain adult material and are usually suitable for even younger audiences.
There is no set size for Doujinshi as each artist or circle is free to make it whatever size they want. Prices for doujinshi can range from $1.00 to as much as several hundred dollars. This form of art has expanded by leaps and bounds over the last decade because it promotes free form art and attracts thousands of talented artists and fans alike.