book reviews 216 https://doi.org/10.1107/S2059798324001451 Acta Cryst. (2024). D80, 216–219 ISSN 2059-7983 Keywords: book review; dynamics; kinetics; structural biology; time-resolved structural analysis. Dynamics and Kinetics in Structural Biology: Unravelling Function Through Time-Resolved Structural Analysis. By Keith Moffat and Eaton E. Lattman. Wiley, New York, 2023, pp. 288. ISBN 978-1- 119-69628-5. Price USD 161 (hardback), USD 128 (Kindle) John R. Helliwell* Department of Chemistry, The University of Manchester, Manchester M13 9PL, United Kingdom. *Correspondence e-mail: john.helliwell@manchester.ac.uk This book is authored by two senior figures active in the topics in the title. They describe in their author biographies that they have worked closely together when Eaton Lattman was lead PI of the USA BioXFEL project and Keith Moffat was Chair of the Advisory Committee. The scope of the book is broad, spanning macromolecular crystallography, solution scattering, cryoEM, and various other biophysical methods and their applica- tions. These together reasonably justify the ‘in structural biology’ portion of the title. ‘Dynamics and kinetics’ is a very broad topic in physical chemistry as well as in computational simulations. A critical, and correct, statement starts the book: Whatever form the experimental sample takes when exploring structural dynamics, the molecules comprising the sample should be demonstrably active. Furthermore this requires the ability to generate and determine short-lived, intermediate structures whose populations vary with time as the biological reaction proceeds. These statements, in effect, determine the content of the rest of the book. This book extends two earlier books entitled Time-resolved Macromolecular Crystal- lography (Cruickshank et al., 1992) and the more general Time-Resolved Diffraction (Helliwell & Rentzepis, 1997). The title of this new book is distinctly different though, spanning two distinct terms ‘dynamics’ and ‘kinetics’. The experimental protocol of one must study the biologically active state of a sample opens the difficult, i.e. even broader, question What is the structural chemistry of the living organism at its temperature and pressure? (Helliwell, 2020). This new book addresses these topics in many ways and in considerable detail. Section 1.5 of the book identifies the focus in all but one of the book chapters as ‘structural dynamics’. Chapter 2 entitled Physical Chemistry of Reactions describes the basics of thermodynamics and kinetics, and those well versed in physical chemistry are instructed to possibly skip this chapter. Section 2.1 declares that these concepts are fundamental to structural dynamics and yet Section 2.2, states that thermodynamics does not deal directly with the 3D structures of molecules or the reactions they engage in. In terms of the foundations of molecular biophysics and structures in motion, I was stimulated to look again at the book by Daune (1999) and I think I will still retain it on my bookshelf. A good resume of studies for cryoMX and cryoEM is given in Section 2.6. A key paper on the limitations of cryostructures is Halle (2004), which is briefly cited but could have been expanded upon. Indeed, Section 2.6 signs off the whole chapter with a swingeing criticism of cryostructures being potentially fatal or requiring cautious analysis for structural dynamics. That conversation over with, Chapter 3 describes The Experiment. Section 3.2.1 is entitled Signal, Accuracy and Systematic Errors. Their definition of accuracy and precision is unconventional. Usually, accuracy is how well two or more different methods determine a quantity, each having their own systematic errors, which are attempted to be minimized. An important highlighted set of results is given in Box 3B, which exemplifies the long-standing experience of the authors gained with synchrotron radiation and then with the Stanford Linac Coherent Light Source (LCLS) whereby identical time points for the same biological system (photoactive yellow protein, PYP) could be compared in a control experiment. Difference electron density signals were