Directed evolution is a method that uses iterative rounds of random mutation and artificial selection to discover new and useful proteins. It allows proteins to adapt to new functions or environments through small mutations. This approach has shown how proteins can evolve rapidly under strong selection pressures and has provided insights into the relationship between sequence and function. Directed evolution has also shown how neutral mutations can set the stage for further adaptation. Proteins have evolved over millions of years to solve a wide range of biological problems efficiently. Directed evolution has been used to extend known protein functions to new environments or tasks and to create new functions. Despite advances, the molecular-level understanding of why one protein performs better than another remains elusive. Proteins can undergo conformational changes and exist as dynamic ensembles of conformers. Mutations far from active sites can influence protein function. Engineering enzymatic activity is particularly challenging because small structural or chemical changes can significantly affect catalysis. Directed evolution has become a common tool for altering and optimizing protein function. It has been used to create new proteins with desired properties, such as a recombinase to remove HIV DNA, a cytochrome P450 enzyme that can hydroxylate alkanes, and a more thermostable lipase. Directed evolution has also improved fluorescent proteins, enhancing their properties like emission and quantum yield. Directed evolution is viewed as a biological optimization process, with the concept of evolution on a fitness landscape in protein sequence space. This framework helps explain directed evolution strategies and the types of trajectories that can traverse the landscape. The fitness landscape can help explain why decomposing a large functional hurdle into smaller steps and exploiting protein modularity are useful strategies. Directed evolution has been applied to other biological components and systems, including RNA, DNA regulatory elements, biosynthetic pathways, and genetic regulatory circuits. Mathematical models can help focus the directed evolution search to components more likely to produce the targeted behavior. Directed evolution has demonstrated how proteins can adapt to new functions and has provided insights into the relationship between sequence and function. Directed evolution has shown that proteins can adapt to new functions through a series of small mutations. The structure of the fitness landscape influences the effectiveness of search strategies. Directed evolution has been used to create proteins with new functions, such as enzymes that can hydroxylate alkanes or enzymes with increased thermostability. Directed evolution has also been used to improve fluorescent proteins and to create new functions in other biological systems. Directed evolution has demonstrated the importance of stability in epistasis and evolvability. It has shown that neutral mutations can shape adaptive pathways during natural evolution. Directed evolution has also been used to address important evolutionary questions about the average effects of mutations, mechanisms of functional divergence, evolvability, and evolutionary constraints. Directed evolution has provided insights into the relationship between sequence and function and has demonstrated how proteins can adapt to new functions. It has also been used to create new proteins with desired properties, such as enzymes that can hydroxylate alkanesDirected evolution is a method that uses iterative rounds of random mutation and artificial selection to discover new and useful proteins. It allows proteins to adapt to new functions or environments through small mutations. This approach has shown how proteins can evolve rapidly under strong selection pressures and has provided insights into the relationship between sequence and function. Directed evolution has also shown how neutral mutations can set the stage for further adaptation. Proteins have evolved over millions of years to solve a wide range of biological problems efficiently. Directed evolution has been used to extend known protein functions to new environments or tasks and to create new functions. Despite advances, the molecular-level understanding of why one protein performs better than another remains elusive. Proteins can undergo conformational changes and exist as dynamic ensembles of conformers. Mutations far from active sites can influence protein function. Engineering enzymatic activity is particularly challenging because small structural or chemical changes can significantly affect catalysis. Directed evolution has become a common tool for altering and optimizing protein function. It has been used to create new proteins with desired properties, such as a recombinase to remove HIV DNA, a cytochrome P450 enzyme that can hydroxylate alkanes, and a more thermostable lipase. Directed evolution has also improved fluorescent proteins, enhancing their properties like emission and quantum yield. Directed evolution is viewed as a biological optimization process, with the concept of evolution on a fitness landscape in protein sequence space. This framework helps explain directed evolution strategies and the types of trajectories that can traverse the landscape. The fitness landscape can help explain why decomposing a large functional hurdle into smaller steps and exploiting protein modularity are useful strategies. Directed evolution has been applied to other biological components and systems, including RNA, DNA regulatory elements, biosynthetic pathways, and genetic regulatory circuits. Mathematical models can help focus the directed evolution search to components more likely to produce the targeted behavior. Directed evolution has demonstrated how proteins can adapt to new functions and has provided insights into the relationship between sequence and function. Directed evolution has shown that proteins can adapt to new functions through a series of small mutations. The structure of the fitness landscape influences the effectiveness of search strategies. Directed evolution has been used to create proteins with new functions, such as enzymes that can hydroxylate alkanes or enzymes with increased thermostability. Directed evolution has also been used to improve fluorescent proteins and to create new functions in other biological systems. Directed evolution has demonstrated the importance of stability in epistasis and evolvability. It has shown that neutral mutations can shape adaptive pathways during natural evolution. Directed evolution has also been used to address important evolutionary questions about the average effects of mutations, mechanisms of functional divergence, evolvability, and evolutionary constraints. Directed evolution has provided insights into the relationship between sequence and function and has demonstrated how proteins can adapt to new functions. It has also been used to create new proteins with desired properties, such as enzymes that can hydroxylate alkanes