Book excerpt: This volume details basic and advanced protocols for both stages of protein engineering: the library design phase and the identification of improved variants by screening and selection. Chapters focus on enzyme engineering using rational and semi-rational approaches. Written in the highly successful Methods in Molecular Biology series format, chapters include introductions to their respective topics, lists of the necessary materials and reagents, step-by-step, readily reproducible laboratory protocols, and tips on troubleshooting and avoiding known pitfalls. Authoritative and cutting-edge, Protein Engineering: Methods and Protocols aims to aid scientists in the planning and performance of their experiments. The chapter 'Functional Analysis of Membrane Proteins Produced by Cell-Free Translation' is open access under a CC BY 4.0 license via link.springer.com.