Over the past decades, numerical and mathematical cognition has transformed from a niche research area into a thriving global field, with contributions spanning diverse populations, methodologies, and theoretical approaches. The 13 articles in this special issue highlight the breadth and depth of contemporary research, addressing topics such as the development of early numeracy skills, the interplay between mathematical and reading processes, the cognitive mechanisms supporting arithmetic and algebra, and the role of visuospatial thinking in expert mathematical reasoning. The contributions exemplify methodological innovation, from longitudinal studies and psychometric evaluations to interdisciplinary theoretical models that integrate numerical and linguistic frameworks. Together, they collectively advance theoretical, applied, and interdisciplinary perspectives. This introduction synthesizes the contributions, demonstrating how they collectively inspire future directions for research on numerical and mathematical cognition. We discuss the broader implications of the work while also contextualizing its development within its historical ties to Canadian experimental psychology and the foundational work of pioneers such as the late Jamie I. D. Campbell, in memory of whom this special issue was conceived. (PsycInfo Database Record (c) 2025 APA, all rights reserved).