As researchers achieve unprecedented technological breakthroughs in natural language processing, the need to understand the systems underlying these advances is more pertinent than ever. BlackboxNLP, now in its sixth iteration, has played an important role in bringing together scholars from a diverse range of backgrounds in order to rigorously study the behavior, representations, and computations of "black-box" neural network models. Our workshop showcases original, cutting-edge research on topics including but not limited to:• analysis of representations via probing and related techniques;• explanation methods such as feature attribution, free-text explanations, or structured explanations; • interdisciplinary methods (e.g., from neuroscience, cognitive science, computer vision, etc.); • interpretable architectures and neural network modules;• mechanistic interpretability and reverse engineering of neural computations; • open-source tools for analysis, visualization, and/or explanation; • opinions about the state of interpretability and explainable NLP; and • targeted evaluations using simplified or formal languages.The sixth BlackboxNLP workshop will be held in Singapore on December 7, 2023, hosted by the Conference on Empirical Methods in Natural Language Processing (EMNLP). 29 full papers and 17 non-archival extended abstracts were accepted for in-person and online presentations, from a total of 66 submissions. This year's workshop will also feature 19 papers on interpretability from the Findings of the ACL: EMNLP 2023, as well as two invited talks and a panel discussion with experts in the field.BlackboxNLP 2023 would not have been possible without the high-quality peer reviews submitted by our program committee, as well as the logistical assistance provided by the EMNLP organizing committee. We gratefully acknowledge financial support from our sponsors, Google and Apple. Our invited speakers, panelists, authors, and presenters have allowed us to put together an outstanding program for all participants to enjoy.Welcome to BlackboxNLP! We look forward to seeing you in Singapore and online.