Welcome to the 16th ACM SIGPLAN International Conference on Software Language Engineering (SLE) held in October 2023 as part of SPLASH 2023. Software Language Engineering (SLE) is a thriving research discipline targeted at establishing an engineering approach to the development, use, and maintenance of software languages, that is, of languages for the specification, modeling and tooling of software. Key topics of interest for SLE include approaches, methodologies and tools for language design and implementation with a focus on techniques for static and behavioral semantics, generative or interpretative approaches (including transformation languages and code generation) as well as meta-languages and tools (including language workbenches). Techniques enabling the testing, simulation or formal verification for language validation purposes are also of particular interest. SLE also accommodates empirical evaluation and experience reports of language engineering tools, such as user studies evaluating usability, performance benchmarks or industrial applications.In 2023, SLE called for submission in four categories: (1) Research Papers, detailing research contributions to SLE, (2) New Ideas and Vision Papers, describing new, unconventional SLE research approaches that depart from standard practice, (3) SLE Body of Knowledge Papers: surveys, essays, open challenges, empirical observations and case study papers which provide a comprehensive description of the concepts and best practices developed by the SLE community, and (4) Tool Papers, focusing on tooling aspects and insights that are likely to be useful to other tool implementers or users in the future.As in 2022, there was a two-phase submission and review process. This gave authors that submitted to the first round an extra opportunity to improve their work based on the comments and feedback of the reviewers. Altogether 40 submissions were received. Double-anonymous review guidelines were adopted for all papers. The reviewers assessed the submissions in terms of their novelty, significance and potential impact, and were instructed to carefully consider weightings across these criteria depending on the paper category.Each submission was reviewed by at least three members of the Program Committee, and ultimately 20 papers were accepted for presentation. The SLE 2023 keynote was given by Crista Videira Lopes from University of California, Irvine.As the Organization Committee, we are indebted to the hard work of the many people who contributed to the success of this year's SLE. Specifically, we would like to acknowledge the work of the Program Committee and for the timely delivery of iii reviews which resulted in a rich and diverse program. We are also grateful to SLE's Steering Committee and the SPLASH organization for their help. Finally, we would like to thank the authors of all submitted papers -you represent the core of the SLE conference, and it is your work that advances the state of the art in software language engineering. We hope that you will enjoy reading the...