All building regulations stipulate that a building project can only be authorised if it complies with public law. This basically presupposes that all requirements of public building law are fulfilled concerning the property to be built on. However, especially in densely built-up city centres, it is difficult if not impossible to comply with these requirements. For this reason, the building codes of the German federal states - with the exception of the Free State of Bavaria - contain regulations on an instrument intended to secure these complex public building law requirements: the so called building obligation that, as a specific institute of building regulations law, seeks to ensure the long term preservation of building law conditions under public law. This study is dedicated to the various legal and practical effects that such a building obligation entails. One focus is on analysing the content, nature and effect of the building obligation. This analysis specifically includes the areas of application under building regulations and building planning law (including nature conservation law and immission control law). Furthermore, the interlocking of the building obligation with civil law security instruments in certain constellations is also part of the study. Finally, the work concludes with a comparison of the special legal situation in the Free State of Bavaria that varies from the rest of Germany, and develops an alternative regulatory model to the building obligation.