1. The PDF4LHC21 combination of global PDF fits for the LHC Run III*We dedicate this paper to the memory of James Stirling, Dick Roberts and Jon Pumplin, all of whom sadly died in the past few years. All three were instrumental in the development and evolution of PDF fitting, Jon for the CTEQ-TEA collaboration and James and Dick for the MSHT collaboration. (1st August 2022) Authors: Ball, Richard D; Butterworth, Jon; Cooper-Sarkar, Amanda M; Courtoy, Aurore; Cridge, Thomas; De Roeck, Albert; Feltesse, Joel; Forte, Stefano; Giuli, Francesco; Gwenlan, Claire; Harland-Lang, Lucian A; Hobbs, T J; Hou, Tie-Jiun; Huston, Joey; McNulty, Ronan; Nadolsky, Pavel M; Nocera, Emanuele R;... Journal: Journal of physics Issue: Volume 49:Number 8(2022) Page Start: Record Type: Journal Article View Content: Available online (eLD content is only available in our Reading Rooms) ↗