The article "UCSF ChimeraX: Tools for Structure Building and Analysis" by Elaine C. Meng, Thomas D. Goddard, Eric F. Pettersen, Greg S. Couch, Zach J. Pearson, John H. Morris, and Thomas E. Ferrin, published in *Protein Science*, discusses the advancements in computational tools for atomic model building, particularly in the context of cryo-electron microscopy (cryo-EM). The authors highlight new methods in the UCSF ChimeraX molecular modeling package that leverage machine-learning structure predictions, likelihood-based fitting in maps, and per-residue scoring to identify modeling errors. ChimeraX also includes tools for analyzing mutations, post-translational modifications, and interactions with ligands. The article covers the latest model-building capabilities in ChimeraX, including community-developed extensions, and emphasizes the program's free availability for noncommercial use. Key features discussed include protein structure prediction using AlphaFold, fitting models into maps, building ligands and solvent, model refinement, and model assessment. The article also explores the use of additional experimental data, such as crosslinking and electron tomography, and general atomic structure building tools. The authors conclude by highlighting the benefits of ChimeraX in automating and improving the accuracy of atomic model building, making it a valuable tool for researchers in structural biology and biochemistry.The article "UCSF ChimeraX: Tools for Structure Building and Analysis" by Elaine C. Meng, Thomas D. Goddard, Eric F. Pettersen, Greg S. Couch, Zach J. Pearson, John H. Morris, and Thomas E. Ferrin, published in *Protein Science*, discusses the advancements in computational tools for atomic model building, particularly in the context of cryo-electron microscopy (cryo-EM). The authors highlight new methods in the UCSF ChimeraX molecular modeling package that leverage machine-learning structure predictions, likelihood-based fitting in maps, and per-residue scoring to identify modeling errors. ChimeraX also includes tools for analyzing mutations, post-translational modifications, and interactions with ligands. The article covers the latest model-building capabilities in ChimeraX, including community-developed extensions, and emphasizes the program's free availability for noncommercial use. Key features discussed include protein structure prediction using AlphaFold, fitting models into maps, building ligands and solvent, model refinement, and model assessment. The article also explores the use of additional experimental data, such as crosslinking and electron tomography, and general atomic structure building tools. The authors conclude by highlighting the benefits of ChimeraX in automating and improving the accuracy of atomic model building, making it a valuable tool for researchers in structural biology and biochemistry.