The assessment of upstream factors is important in population-based nursing practice. The aim of this concept analysis is to enhance understanding of upstream factors and articulate a definition linked to the Conceptual Model for Nursing and Population Health. Upstream factors are thus defined as established conditions related to economic, social, and physical environments that occur outside the health care system, in the communities where people live, and contribute indirectly to the health outcomes for groups of individuals through multiple causal pathways. This concept analysis highlights the need for middle-range theory to guide nursing assessment and contributes to conceptual model evaluation.