Ownership of real property is not vertically restricted (clearly) in many countries, i.e. the right of use is based on the situation on the surface level. Underground and overground premises may be brought for the use of a third party by establishing a usufruct restricting the right to use the property. However, in many countries it is possible to establish three-dimensional real properties and get also a market for 3D properties. In Finland the 3D land use in buildings is arranged rather far through a third way with the limited company system. There is specific legislation for housing stock companies, which is also applied to mutual real estate stock companies. In a housing stock company the ownership of a shareholder entitles to the possession of certain premises (apartments) stated in the articles of association. The share certificates may be pledged as security like the shares of an ordinary limited company. The share certificates, i.e. the apartments, have an active market and they are quite liquid. It can be said that the 3D land use in built up properties is functioning very well in Finland. There are, however, some problems when there is a need to use the space under or over an existing real property and when there is also a need to mortgage that right.