In view of the incessant growth of data and knowledge and the continued diversifi- tion of information dissemination on a global scale, scalability has become a ma- stream research area in computer science and information systems. The ICST INFO- SCALE conference is one of the premier forums for presenting new and exciting research related to all aspects of scalability, including system architecture, resource management, data management, networking, and performance. As the fourth conf- ence in the series, INFOSCALE 2009 was held in Hong Kong on June 10 and 11, 2009. The articles presented in this volume focus on a wide range of scalability issues and new approaches to tackle problems arising from the ever-growing size and c- plexity of information of all kind. More than 60 manuscripts were submitted, and the Program Committee selected 22 papers for presentation at the conference. Each s- mission was reviewed by three members of the Technical Program Committee.