When married couples buy a house, typically both names are put on the title, or deed, and both are considered the legal co-owners of the home. However, that is not the only way to legally co-own a home. In fact, many people that only own half a duplex actually co-own a home and don't even realize it.
Also, it is not too uncommon for friends and non-married couples to buy homes together, and this can be where things get more complicated. Questions arise such as: