This EPTCS volume contains the proceedings of the 16th Workshop on Quantitative Aspects of Programming Languages and Systems (QAPL 2019) held in Prague, Czech Republic, on Sunday 7 April 2019. QAPL 2019 was a satellite event of the European Joint Conferences on Theory and Practice of Software (ETAPS 2019). QAPL focuses on quantitative aspects of computations, which may refer to the use of physical quantities (time, bandwidth, etc.) as well as mathematical quantities (e.g., probabilities) for the characterisation of the behaviour and for determining the properties of systems. Such quantities play a central role in defining both the model of systems (architecture, language design, semantics) and the methodologies and tools for the analysis and verification of system properties. The aim of the QAPL workshop series is to discuss the explicit use of time and probability and general quantities either directly in the model or as a tool for the analysis or synthesis of systems. The 16th edition of QAPL also focuses on discussing the developments, challenges and results in this area covered by our workshop in its nearly 20-year history.