PODIO is a C++ library that allows the creation of event data models and efficient I/O code for HEP experiments. It does so by avoiding deep-object hierarchies and virtual inheritance. On the other hand, HDF5 is a data format that allows one to manage extremely large and complex data collections. Due to its versatility as a data model and rich set of performance features, it is an ideal format to store PODIO data in. The aim of this project is to implement an HDF5 backend for PODIO.