This volume contains a selection of the contributed papers from the 27th Biennial Meeting of the Philosophy of Science Association, PSA 2021, which will be memorable as the PSA that was postponed for the COVID-19 pandemic. At the time of completing this volume, the postponed meeting is planned to occur in Baltimore, Maryland, November 11–14, 2021—rescheduled from November 2020. A second proceedings volume containing selected symposium papers and Alison Wylie’s presidential address will be published next year.

Many people deserve thanks for their significant contributions to the production of this volume. Thank you, first, to the many people who submitted papers. PSA 2021 received 343 contributed papers, from which the program committee selected 171 (50%) for presentation at the meeting and just 42 (12.5%) for publication in this volume. The excellent and wide-ranging work contributed to this meeting is a testament to the current strength of our discipline.

I am also extremely grateful to the members of the PSA 2021 Program Committee for their enormous investment of time and effort spent reading and evaluating contributed papers and the advice they provided throughout the review process. It is worth noting that the most intense period of our review coincided with the global stress, disruption, illnesses, and losses of March–May 2020.

The program committee includes:

Valia Allori (Northern Illinois University)

Holly Andersen (Simon Fraser University)

Karim Bschir (University St. Gallen)

Daniel Burnston (Tulane University)

Julia Bursten (University of Kentucky)

Adrian Currie (University of Exeter)

Melinda Fagan (University of Utah)

Joyce Havstad (University of Utah)

Yoichi Ishida (Ohio University)

Jennifer Jhun (Duke University)

Colin Klein (Australian National University)

Olimpia Lombardi (University of Buenos Aires)

John Mathewson (Massey University)

Inmaculada de Melo-Martín (Cornell University)

Eric Pacuit (University of Maryland, January–February 2020)

Richard Pettigrew (University of Bristol)

Darrell Rowbottom (Lingnan University)

Jacqueline Sullivan (Western University)

Jonathan Tsou (Iowa State University)

Giovanni Valente (Politecnico di Milano)

David Wallace (University of Pittsburgh)

Robert Wilson (University of Western Australia)

Outgoing PSA Executive Director Jessica Pfeifer also deserves our thanks for her strong leadership and tireless work planning PSA 2021, including through the confusion wrought by COVID-19 disruptions, as well as for her responsible stewardship of PSA since 2013. You can find a tribute slideshow to Jessica’s leadership on the PSA website at https://philsci.org/tribute_to_jessica_pfeifer.php. Thank you also to incoming PSA Executive Director Ryan Feigenbaum, who took the reins of PSA during worldwide tumult, facing two biennial meetings in as many years, and is nonetheless already masterfully guiding PSA into its next chapter. Thanks also to Sarah Lipman, assistant director of PSA during most of the preparations for PSA 2021, and Jonathan McKinney and Taraneh Wilkinson, the subsequent PSA assistant directors in the leadup to the meeting.

Kevin Elliott, the PSA 2018 program chair, was generous with his helpful advice and encouragement, and he and Wendy Parker (PSA 2016 chair) deserve credit for documenting the processes of their program committees, facilitating greater consistency and iterative improvements across successive program committees.

I also owe my thanks to the Philosophy of Science editorial team, particularly Editor-in-Chief Andrea Woody and Managing Editor Kayla Mehl-Hutchinson. It was a pleasure to work with both of them throughout the production process; their guidance and support were always both speedy and valuable. It was great to see behind the scenes of the PSA’s well-run journal.

Finally, I am grateful to the PSA Governing Board, and especially PSA President Alison Wylie, for the opportunity to serve as PSA 2021 program chair, financial support enabling me to have a reduced teaching load while in the role, and their unparalleled leadership through a time of many PSA transitions as well as pandemic disruptions.

Thank you, once again, to everyone who contributed to PSA 2021 and to the authors who wrote the papers comprising this volume. The most rewarding aspect of serving as program chair has been learning about the wide range of impressive scholarship produced by members of PSA.