This book constitutes the refereed proceedings of the 19th European Workshop on Computer Performance Engineering, EPEW 2023, and 27th International Conference on Analytical and Stochastic Modelling Techniques and Applications, ASMTA 2023, held in Florence, Italy, in June 2023. The 26 papers presented in this volume were carefully reviewed and selected from 35 submissions. The papers presented at the workshop reflect the diversity of modern performance engineering. The sessions covered a wide range of topics including robustness analysis, machine learning, edge and cloud computing, as well as more traditional topics on stochastic modelling, techniques and tools.