It is often difficult to say exactly from what particular Western country something originated, so this thread will be about all the cultural influences in Japan from the West. I decided to start this thread as people were starting going off-topic about the West in the thread How much of Japan's traditional culture comes from China ?
Food
The dishes listed here are only those completely integrated in modern Japanese culture, not all those found in Japan. It means that the Japanese have developed their own version (e.g. nori-tarako pasta) or it has become part of normal "home-cooking".
Tempura
Pasta
Pizza
Crepes
Gratin
Pot-au-feu
Ratatouille
Potage, consome, minestrone
Chocolate, pralines
Dairy products (including pudding, cheese, cheese cakes, etc.)
Western cakes (Castella, brownie, apple pie, sponge cake...)
Bakery and pastries (bread, croissant, chou a la creme, eclair, turnover...)
...
Festivals & traditions
Valentine's Day
Mother's Day
Father's Day
Halloween
Christmas
New Year on 1 January (Japan used to follow the Chinese calendar and New Year until Meiji)
Technologies
It would be impossible to list everything here, so I limited myself to those that had a great effect on modern Japanese culture (for example, a lot of electronic goods were not invented in Japan, but were improved and mass-manufactured by the Japanese).
Automobiles
Airplanes
Computers
Video games
TV
Radio
CD
Camera
Watches
Phone & mobile phone
Concrete
Glass/plastic windows (as opposed to the traditional paper ones)
Hinged doors (as opposed to sliding doors)
...
Sports
Rather than listing all Western sports practised in Japan, I limited myself to those playing a major role in modern culture (e.g. those played in schools or in which the Japanese excel in international competitions).
Baseball
Football
Volleyball
Badminton
Tennis
Table Tennis
Marathon
Athletics
...
Other cultural elements
Westerns-style clothes (—m•ž)
Western hairstyles
Western-style toilets (which the Japanese improved with some gadgets)
Western music (from classical to pop and rock)
Western movies (not just Hollywood)
Western-style tables, chairs, forks, spoon, knives, glasses...
Card games (poker, bridge...)
...
Interestingly, there are Western things that never really became popular in Japan. For example :
- board games (like Monopoly, Stratego or Trivial Pursuit)
- hinged windows (all Japanese houses seem to have sliding windows, although most modern houses now have hinged doors).
Bookmarks