A large amount of Chinese words was adapted together with the Chinese writing system in the 5th century and afterwards. Chinese loan words are naturally written in kanji (Chinese characters).

In more recent times, many words were also borrowed from Portuguese, Dutch, German (especially from the fields of medicine and mountaineering), French and Italian (especially from the fields of music and food), and, of course, English which is the origin of most modern loan words. Non Chinese loan words are written in katakana.

Loan words are often heavily Japanized in various ways (see below), which is a complicating factor not only for students of the Japanese language but also for Japanese students of foreign languages:

• The pronunciation of loan words is Japanized, and sometimes quite different from the original pronunciation: e.g. curtain=kaaten, elevator=elebeetaa, girl=gaaru.

• Many loan words get abbreviated in ways they do not get abbreviated in the original language: e.g. suupaa=supermarket, kilo=kilometer (and kilogram), depaato=department store, waapuro=word processor.

• The meanings of some loan words do not correspond with the words' original meanings: e.g. "manshon" from the English "mansion" means "condominium".

• And finally, some "loan words" are actually Japanese creations rather than loan words. For example, "salaryman" is a Japanese word for a typical Japanese company worker, while the "walkman" even found its way back into English dictionaries.