This chapter examines the evolution of cognitive abilities across the lifespan, highlighting key developmental milestones and the factors that shape cognitive growth and decline. It begins by outlining the stages of cognitive development from infancy through adolescence, emphasizing critical achievements such as object permanence, symbolic thought, and the progression from concrete to abstract reasoning. As individuals transition into adulthood, their cognitive abilities peak and later gradually decline—fluid intelligence tends to diminish, whereas crystallized intelligence often remains stable or improves. This chapter introduces the concept of cognitive reserve, which buffers against age-related decline through factors such as education, occupational complexity, and continuous cognitive engagement. Finally, it reviews interventions aimed at maintaining cognitive health during aging, including physical exercise, cognitive training, diet, social engagement, and sleep hygiene, underscoring a holistic approach to promote brain resilience and longevity. These insights provide valuable implications for educators, clinicians, and policymakers working to optimize cognitive function throughout life.