This chapter presents a range of concepts and findings from the fields of information-processing research and leader cognition and to explore their importance for understanding the role that processes of expertise play in public sector-leader performance. It provides two primary cognitive components known to underpin expertise-knowledge and mental models-and further reviews and integrates existing research regarding the role of expertise in leader performance. The gradual accumulation of these various forms of knowledge typically leads to the forming and consolidating of mental models. Having highly contrasting mental models that contain varying knowledge structures could potentially cover a larger number of particular domains relevant to organizational functioning. Some additional individual attributes that might also be related to effectively addressing public leadership problems include varying degrees of leadership expertise, technical expertise, expertise in other domains, intelligence, general affect or disposition, and personal distance.