The 13th Theoretical Aspects of Software Engineering Symposium (TASE 2019) will be held in Guilin, China in July, 2019. TASE is an international symposium that aims to bring together researchers and developers from academia and industry with interest in the theoretical aspects of software engineering. Modern society is increasingly dependent on software systems that are becoming larger and more complex. This poses new challenges to current software engineering methodologies that need to be enhanced using modern results from theoretical computer science. We invite submission of research papers on topics covering all theoretical aspects of software engineering, including those describing applications of theoretical computer science in industrial applications and software engineering methodologies. TASE 2019 is the 13th in the TASE series. The past TASE symposiums were successfully held in Shanghai ('07), Nanjing ('08), Tianjin ('09), Taipei ('10), Xi'an ('11), Beijing ('12), Birmingham ('13), Changsha('14), Nanjing('15), Shanghai('16), Nice('17), Guangzhou('18).