Platform O.N.E. is an OSGi based application platform of Deutsche Telekom. The talk gives an overview of the key architectural concepts, design patterns and ideas behind the Platform O.N.E. The talk is practically orientated and will be accompanied by slides and a live coding demo with a running example. The core idea behind the Platform O.N.E. is to provide easy access for third party users (e.g. mobile-apps, web-applications, or other kind of clients) to internal services of Deutsche Telekom. The internal services are exported by platform modules as REST or SOAP services. A platform module provides an easy way to enhance a service with features like: authentication, authorization, security, billing, logging, profiling, monitoring etc. For module implementation the platform provides: an OSGi based run-time, a standard module design, a maven based build process and a set of Platform O.N.E. specific OSGi services. The talk consists of three parts. The fist part gives an overview of the platform architecture and the OSGi technologies used. The second part discusses the design of a platform module and shows the advantages arising from modular design and the use of an OSGi based platform. The second part will be presented on a running example module as a live coding demonstration. The final part of the talk summarizes the key learnings and discusses which OSGi technologies might play a role in the future development of Platform O.N.E.