Several factors influence the degree of gene reuse during repeated adaptation, offering insights into how evolution is constrained at the genomic level. Although numerous studies have identified signatures of genomic repeatability in adaptive evolution, there is a lack of synthesis regarding the statistical tests used to quantify gene reuse across lineages. In this review, we survey published studies to (i) compile a comprehensive list of statistical indices available for quantifying gene reuse during adaptation and (ii) compare patterns of the degree of gene reuse across 120 taxa and four trait categories. Our analysis reveals that currently gene reuse studies are biased in focal species and traits commonly studied. Importantly, relatively few genomic loci contribute to repeatability and this variability is context dependent. By summarizing currently available indices to quantify gene reuse, we propose a straightforward methodological framework for designing studies that quantify gene reuse during repeated adaptation. While this review advances our understanding of the degree of gene reuse, we emphasize the need for broader and more inclusive research to uncover the factors driving variability in gene reuse during adaptive evolution.