Executive functions represent a set of higher-order cognitive skills essential for day-to-day adaptation. This introductory chapter aims to provide a comprehensive overview of these functions, exploring their definitions, components, and relevance. Initially, the primary theoretical models of executive functions are examined, outlining their fundamental characteristics. Subsequently, the relationship between executive functions and the stages of human development, from childhood to adulthood, is analyzed, highlighting their influence on academic, professional, and social performance. Additionally, the underlying neurobiological bases of executive functions are investigated, focusing on key brain regions involved, such as the dorsolateral prefrontal circuit, the orbitofrontal circuit, and the anterior cingulate circuit, emphasizing their specific roles in cognitive and emotional regulation. Finally, neuropsychological assessments of executive functions and their practical implications in various contexts, such as educational, clinical, and occupational, are discussed, emphasizing the importance of intervention and training strategies to promote both the development and maintenance of these skills across different segments of the population.