Older persons and aging are the focus of gerontological research. This chapter presents several key issues that uniquely affect an older population. A clear understanding of normative and non-normative age-related changes in later life is essential to aging research. These changes are reviewed to paint a clear picture of older persons. The non-normative age-related changes include: sensory changes, physical and functional changes and cognitive changes. Researchers must consider their own role in the study and the involvement of older persons as co-researchers. Settings also vary with older peoples' participation in studies in places across the continuum of care—in the community, assisted living, skilled or memory care, and hospice. Researchers must be aware of cultural norms and appropriate ways to study aging and older people across cultures. Time, itself, plays multiple roles in studies about aging. The chapter discusses the age-period-cohort issue of time in aging studies.