A mud room or mudroom is a room which is built into some houses to act as a barrier between outdoors and indoors. Especially in regions with wet, muddy winters, a mud room can be a useful addition as it helps to keep the house clean. In addition, the mud room constitutes a clear boundary between indoors and out, which can be a useful reminder for animals and exuberant members of the household.

Generally, a mud room has easily cleaned floors made in materials like tile, concrete, or linoleum. In extreme cases, a mud room may even have a drain in the floor to make sluicing the floor very easy. A well designed mud room also has ample hooks and racks for damp, wet clothing, as well as racks or cubbies for shoes. In addition, benches for people to sit on while they remove their shoes are not uncommon. All of these measures are designed to encourage people to remove sodden or dirty layers before entering the house.

Generally, mud rooms are not the primary entrances of homes, since they tend to be informal in nature. A side or backyard door usually leads into the mud room, and family members may be encouraged to use it while guests are welcomed through the front door. Often, the washer and dryer are also tucked into the mud room, for the sake of convenience. A mud room which doubles as a laundry room is handy, since wet baskets of clothing do not need to be carried through the house to outdoor clotheslines, and soiled or wet clothing can be immediately dumped into a washer without being tracked through the house.

In addition to being useful in inclement weather, a mud room is also very handy for households with animals such as horses. Soiled clothing can be removed in the mud room so that scents and dirt are not tracked into the house, while animals such as farm dogs may be encouraged to wait in the mud room while their owners take care of business in the house. For animals who are allowed into the house, a mud room is a good staging area for washing off dirty paws and bodies.

Since a mud room bridges the space between indoors and outdoors, a household without a mud room can easily add one, as it simply requires building an addition onto a home, rather than doing extensive structural work inside the home itself. Generally, it is recommended that people work with contractors when installing additions to their homes, to ensure that the addition conforms with local building codes. However, economy minded home owners could work with a contractor to draw up the plans and do the basic framing, and finish up the mud room on their own.