Smart mobile devices such as mobile phones or PDAs have by far outnumbered desktop computers or portable notebooks. Using them as a computing platform has a big potential as they support both, mobility of humans and their ubiquitous service demands. Developing programs for smart mobile devices differs from developing programs for more traditional computing platforms such as desktop computers: Capabilities such as their location dependency and their availability can be used to create entirely new applications; on the other side, constraints in terms of processing power, memory limitations and UI restrictions are additional challenges which must be aware to everyone designing applications for this type of devices. This lecture will give an overview of the enhanced capacities and how to use them, as well as how to take care of the constraints. The predominant methodology in use will be a comparison between the "traditional way" of solving common application layer problems and the "smart mobile device way" of solving them. For this purpose, two different editions of the Java programming language will be used to show (and exercise) typical differences: The Standard Edition (J2SE) and the Mobile Edition (J2ME, in particular MIDP/CLDC).