"Traditionally, Japanese is written in a format called "tategaki". In this format, the characters are written in columns going from top to bottom, with columns ordered from right to left. After reaching the bottom of each column, the reader continues at the top of the column to the left of the current one. This copies the column order of Chinese."
"Modern Japanese also uses another writing format, called "yokogaki". This writing format is horizontal and read left to right."
http://en.wikipedia.org/wiki/Japanese_writing#Direction_of_writing
"Many East Asian scripts can be written horizontally or vertically. The Chinese, Japanese and Korean scripts can be oriented in either direction, while the traditional Mongolian script and its offshoots (like Manchu) are written vertically."
"Japanese, horizontal writing is called yokogaki (横書き, "horizontal writing", also known as yokogumi, 横組み) and vertical writing is called tategaki (縦書き, "vertical writing", also known as tategumi, 縦組み)."
"Traditionally, Chinese, Japanese, and Korean are written vertically in columns going from top to bottom and ordered from right to left, with each new column starting to the left of the preceding one. The stroke order and stroke direction of Chinese characters (hanzi in Chinese, kanji in Japanese, hanja in Korean), Japanese kana, and Korean Hangul all facilitate writing in this manner. In addition, writing in vertical columns from right to left facilitated writing with a brush in the right hand while continually unrolling the sheet of paper or scroll with the left. In modern times, it has become increasingly common for these languages to be written horizontally, from left to right, with successive rows going from top to bottom, under the influence of European languages such as English."
"Horizontal text originally came in to Japanese in the Meiji era when the Japanese tried to print dictionaries for Western languages. Initially the dictionaries were printed in a mixture of horizontal Western and vertical Japanese text, which meant the book had to be rotated ninety degrees in order to read the Japanese. Because this was unwieldy, the idea of yokogaki came to be accepted. One of the first publications to partially use yokogaki was a German to Japanese dictionary (袖珍挿図独和辞書, Shūchinsōzu Dokuwa Jisho, "pocket illustrated German to Japanese dictionary") published in 1885 (Meiji 18)."
"At the very beginning of the change to horizontal alignment in Japan, in the Meiji era, there was a short-lived form called migi yokogaki (右横書き, literally "right yokogaki"), in contrast to hidari yokogaki, (左横書き, literally "left yokogaki"), the current standard. This resembled the right-to-left horizontal writing style of languages such as Arabic with line breaks on the left hand side of the page. It was probably based on the traditional single-row right-to-left writing. This form was never widely used, and has not survived."
"Both horizontal and vertical writing are used in Japan, as well as in Hong Kong, Macau and Taiwan where the Traditional Chinese orthography is used. Traditional Chinese is also used in mainland China in a few limited contexts, such as some books on ancient literature, or as an aesthetic choice for some signs on shops, temples, etc. In those contexts, both horizontal and vertical writing are used as well."
"Vertical writing is commonly used for novels, newspapers, comics, and many other forms of writing. Because it goes downwards, vertical writing is invariably used on the spines of books. Some newspapers combine the two forms, using the vertical format for most articles but including some written horizontally, especially for headlines. Musical notation for some Japanese instruments such as the shakuhachi is written vertically."
"Horizontal writing is easier for some purposes; academic texts are sometimes written this way since they often include words and phrases in other languages, which are more easily incorporated horizontally. Scientific and mathematical texts are nearly always written horizontally, since in vertical writing equations must be turned sideways, making them more difficult to read."
"Similarly, English language textbooks, which contain many English words, are usually printed in horizontal writing. This is not a fixed rule, however, and it is also common to see English words printed sideways in vertical writing texts."
"Computer text is usually presented in horizontal format; see _Japanese language and computers_."
"Business cards in Japan (meishi) are often printed vertically in Japanese on one side, and horizontally in English on the other. Postcards and handwritten letters may be arranged horizontally or vertically, but the more formal the letter the more likely it is to be written vertically. Envelope addresses are usually vertical, with the recipient's address on the right and the recipient's name in the exact centre of the envelope."
http://en.wikipedia.org/wiki/Horizontal_and_vertical_writing_in_East_Asian_scripts