Smalltalk is an exciting object-oriented language in which even primitive values are uniformly handled as normal objects described by classes that one can browse and extend. Smalltalk was born during the seventies, but the ideas behind currently available implementations are still modern and innovative. Smalltalk benefits from being a highly expressive language in which complex and powerful systems can emerge from the composition of simple building blocks. Thanks to its dynamic nature, fast prototyping and agile software development are made possible. Smalltalk also benefits from having powerful meta-programming facilities. A program is able to query and to change its own structure and behavior. Smalltalk is not only a language but also an interactive system that is implemented in Smalltalk and that can be customized according to users needs. This special issue presents four extended versions of research papers from the third International Workshop on Smalltalk Technologies (IWST) that was organized at Edinburgh on September 2011.