Humans can focus their attention narrowly (e.g., to read this text) or broadly (e.g., to determine which way a large crowd of people are moving). This Element comprehensively considers attentional breadth. Section 1 introduces the concept of attentional breadth, while Section 2 considers measures of attentional breadth. In particular, this section provides a critical discussion of the types of psychometric evidence which should be sought to establish the validity of measures of attentional breadth and reviews the available evidence through this lens. Section 3 considers the visual task performance consequences of attentional breadth, including prescribing several key methodological criteria that studies that manipulate attentional breadth need to meet, as well as a discussion of relevant theories and avenues for future theoretical development. Section 4 discusses the utility of the exogenous-endogenous distinction from covert shifts of attention for understanding the performance consequences of attentional breadth. Finally, Section 5 provides concluding remarks.