dot JP (.jp) - Domain Names

Regulations and management of ".jp" domains in Japan is provided by an organization called Japan Registry Services Co., Ltd. (JPRS).

JPRS has formal recognition from ICANN.

According to the FAQs on JPRS site, in order to be eligible registering a ".jp" domain name, you need a permanent postal address in Japan.

"Any individual, group or organization having a permanent postal address in Japan is eligible for registration of General-use JP Domain Name."

".jp" domains can be registered by individuals, groups, etc.

".co.jp" domains, on the other hand, can be only registered by companies.
This is the reason why most company websites in Japan are on ".co.jp" domains, including big ones like www.google.co.jp or www.yahoo.co.jp

I’ve recently read about a trend in Japan, where even companies prefer registering ".jp" domains rather than ".co.jp", the reason being: they are cheaper, and URLs are shorter.