This volume is a documentation of the main results in the research area "In- gration of Software Speci'cation Techniques for Applications in Engineering." On one hand it is based on the Priority Program "Integration von Techniken der Softwarespezi'kation fur ] ingenieurwissenschaftliche Anwendungen," short Soft- Spez, oftheGermanResearchCouncil(DFG). Ontheotherhanditcontainsnew contributions of international experts in this research area, some of which were presented at the third international workshop INT 2004 on "Integration of Sp- i'cation Techniques for Applications in Engineering." INT 2004 was launched as a satellite event of ETAPS in Barcelona, the "European Joint Conferences on Theory and Practice of Software." The Priority Program SoftSpez was initiated by W. Brauer, M. Broy, H. Ehrig, H. J. Kreowski, H. Reichel, and H. Weber concerning di'erent aspects from computer science, and by E. Schnieder and E. Westk] amper concerning two main application areas in engineering, namely "Tra'c Control Systems" and "Production Automation." After acceptance of SoftSpez by the German Research Council for the period of 1998-2004 a call for speci'c projects within this priority program was launched, where 11 projects from about 75 project proposals were accepted for a period of two years. Since 1998 each year the main research proposals and results of the projects have been presented at an annual colloquium of the priority program, and every two years the projects have been evaluated by an independent group of referees appointed by the G- man Research Council. At this point we would like to thank A.