Customs you need to know before visiting Japan

5. Thresholds
Take off your shoes at the entrance to all homes, and most businesses and hotels. Usually a rack will be provided to store your shoes, and pair of guest slippers will be sitting nearby; many Japanese bring a pair of indoor slippers just in case, though.
Never wear slippers when you need to step onto a tatami mat (used in most Japanese homes and hotels; the standard unit of measurement for area even today), and be careful to remove the toilet slippers waiting for you in the bathroom.
It is extremely bad form, for example, to reenter the main room of a house wearing slippers that have been running across dirty linoleum.