This chapter evaluates various methods for inferring how phenotypes/genotypes influence population dynamics, including extensions of the year-by-year tracking approach used in analyzing the eco-to-evo side of eco-evolutionary dynamics. It provides a detailed outline of the various possibilities, including complexities that move beyond population dynamics. The chapter examines how maladaptation resulting from environmental change might decrease individual fitness and contribute to population declines, range contractions, and extirpations. It considers the extent to which contemporary evolution helps to recover individual fitness and population size, which might then make the difference between persistence versus extirpation and range expansion versus contraction. A final analysis asks how phenotypic variation within populations and species influences population dynamics.