This paper reviews research on expertise in design, focusing on expert performance. It discusses the development of expertise, which requires dedicated practice and experience, and highlights differences between expert and novice designers. Experts often use solution-focused strategies, while novices tend to approach problems in a more structured, step-by-step manner. Studies show that experts can quickly identify and develop solution concepts, and they often work with a broader range of ideas, even when faced with challenges. However, many experts tend to stick to initial concepts and are reluctant to abandon them, even when they are not satisfactory. This behavior is sometimes seen as unprincipled, but it may be a natural part of the design process. Expert designers are also characterized by their ability to work with multiple aspects of a problem simultaneously and to switch between different modes of activity. They often use 'opportunistic' strategies, deviating from a structured plan when it is more efficient. This flexibility is important in the design process, especially when dealing with ill-defined problems. Studies of outstanding designers suggest that they often have a strong commitment to their work and set high standards for themselves. They also tend to frame problems in a way that encourages the development of creative solutions. The paper also discusses the importance of problem framing in design, where designers actively define the problem and guide the search for solutions. This is a key aspect of expert design behavior. The paper concludes that understanding design expertise requires a deeper exploration of the cognitive processes involved in design, and that more research is needed to fully understand how expertise develops in design. It also emphasizes the need for a better understanding of design cognition and the role of experience in shaping expert design behavior.This paper reviews research on expertise in design, focusing on expert performance. It discusses the development of expertise, which requires dedicated practice and experience, and highlights differences between expert and novice designers. Experts often use solution-focused strategies, while novices tend to approach problems in a more structured, step-by-step manner. Studies show that experts can quickly identify and develop solution concepts, and they often work with a broader range of ideas, even when faced with challenges. However, many experts tend to stick to initial concepts and are reluctant to abandon them, even when they are not satisfactory. This behavior is sometimes seen as unprincipled, but it may be a natural part of the design process. Expert designers are also characterized by their ability to work with multiple aspects of a problem simultaneously and to switch between different modes of activity. They often use 'opportunistic' strategies, deviating from a structured plan when it is more efficient. This flexibility is important in the design process, especially when dealing with ill-defined problems. Studies of outstanding designers suggest that they often have a strong commitment to their work and set high standards for themselves. They also tend to frame problems in a way that encourages the development of creative solutions. The paper also discusses the importance of problem framing in design, where designers actively define the problem and guide the search for solutions. This is a key aspect of expert design behavior. The paper concludes that understanding design expertise requires a deeper exploration of the cognitive processes involved in design, and that more research is needed to fully understand how expertise develops in design. It also emphasizes the need for a better understanding of design cognition and the role of experience in shaping expert design behavior.