Property ownership in Germany, both in terms of houses as well as in terms of the land these houses are build on, was easy to determine and manage in Germany after the Second World War because since the days of the German Empire, – in addition to tax records since immobile property such as land and houses are taxed – every German municipality has two bureaucratic agencies that manage these things: The Katasteramt and the Grundbuch.

The Katasteramt or Vermessungsamt is basically the land registry office. It's a public agency maintained by municipalities that surveys the land of the municipality and includes a registry about which plots of land can be used for what purpose. If you own a piece of land in Germany, it is possible that you might not be able to build on it because it is designated as land for agricultural purposes or it might an area that is prone to flooding, avalanches or similar depending on where you live. These circumstances and whether a piece of land is designated as land for building, land used for agriculture and so forth as well as the exact boundaries of a piece of land are all registered with the Katasteramt. "Kataster" is the word for a registry concerning space and this is what a modern Kataster looks like. As you can see, it charts plots of land with a number on a map and maintains further information on these plots you can look up with the numbers.

Who owns the land and what is on it as well as potential financial obligations to said land or house on it (meaning if there is a chance that a bank might request said land as security) is registered with in the Grundbuch ("land book"), another registry maintained by the Amtsgericht, the local courts. Every piece of land, including what is on said land, has an entry in the Grundbuch and it also registered who owns said land and what is on it as well as its size and other features. Every time you sell or buy a piece of land or a house, the sale/buy only becomes fully completed once the new property relations are registered with the Grundbuch.

This follows a fundamental principle in German property law already established since medieval times and codified in the German Empire called the principle of publicity. This legal principle says that when it comes to the property of immobile things, property relations need to be publicly apparent and accessible. Every person in Germany can, if they can show justified interest, take a look in the Grundbuch to see who owns which piece of land, its exact boundaries, and who owns what is on it.

While during WWII certain Grundbücher were destroyed by fighting, bombing, and because of flight and expulsion, these are not the only copies. Usually the owner of land or a house also receives his or her relevant entry in the Grundbuch and since 1935 all local courts were required to send copies of their Grundbücher to the central archives of the federal German state they are in where they are kept in their own archive. Furthermore, since Grundbücher are of such importance with regards to property relationships, they are required to be kept in fire proof safes, meaning that in some cases, even when a bomb hit a local court's building they sometimes survived.

In this sense, managing property relations, determining the boundaries of land and so forth in post-1945 Germany was a fairly straight-forward process in the sense that the property relations as they were in May 1945 were easy to research and determine. A quick research in the German legal database determines that only very few locals experienced a total destruction of the Grundbücher and that with the help of property owners and the records kept in various central archives (and the help of former officials) it was a fairly straight-forward, if sometimes time consuming, process to reconstruct the Grundbücher.

The legal battles in connection to the entries in the Grundbuch however, mainly focused on stolen Jewish property, meaning where Jews and other victims of the Nazis had been forced to sell or gift their property to Germans or the German state. While the Allied powers did introduce provisions that no Nazi criminal was to profit form their criminality and therefore the occupying power had the right to requisition property, which was considered such profit (hence the state of Bavaria still owning Hitler's former house in Munich), handing back such property to its original Jewish owners worked only if these former owners came forward and claimed it, meaning if they weren't dead, which due to the Holocaust was often the case. This meant that in many, many cases, people who had profited from the Nazis' Aryanization campaign, especially those who bought property the German state had expropriated from Jews, were able to keep said property until this day.

In short, Grundbücher and the registries in the Katasteramt made it rather easy to determine and manage property relations after WWII and additionally, they are a frequently used source for historians for various purposes, especially for writing social histories of Germany since with those registries property of land and buildings can be traced rather far back in history.