Only some of your walls are needed to hold up your house. These are called bearing walls. The rest of the walls, the partition walls, are simply there to divide rooms. You can remove either type of wall, but if the wall is load bearing, you have to take special precautions to support the structure during removal, and to add a beam or other form of support in its place. Ceiling or floor joists that are spliced over the wall, or end at the wall, mean the wall is bearing. Look for these from the attic. Walls that are stacked may be load bearing. Find these by measuring or by studying a floor plan of your house. In some cases, you may not be able to tell for sure whether a wall is bearing. If you're not sure, hire a contractor or structural engineer to help you figure it out.