The primary motivation for writing the thesis Modern Object Oriented XML API for PHP was absence of PHP API which would be easy to use, correct and complete. This thesis analyzes the flaws of current PHP APIs and describes how they are solved in modern APIs in other programming languages. It also presents an in-depth description of XML language and its associated standards. Using the knowledge gained from the analysis, the thesis proposes a new API called phpxom based on Java API XOM. The API is then implemented according to the proposal. The resulting PHP library has all the required features -- easiness of use, correctness and completeness. Finally, the thesis analyzes the possibility to implement phpxom as a PHP extension written in C language, which would make it faster and lower its memory requirements.