By revealing deeper meanings and connecting the visitor to the resource, interpretation strives to accomplish a number of goals. Interpretation can increase knowledge of a program's topic, change the visitor's attitude toward something, change future behaviors, and increase appreciation for a place and its resources. While literature exists professing best practices for interpretation, little empirical support is present in the research literature to validate these practices' individual links to desired outcomes. This study empirically identifies attributes of the interpreter that statistically linked to visitor outcomes. We tracked 31 interpreter attributes and 10 intended outcomes of interpreters in 376 live interpretive programs in 24 units of the U.S. National Park Service (NPS) and conducted visitor surveys immediately following the programs. This research addresses the following question: Which interpreter attributes most consistently lead to desired outcomes? Our research shows that the interpreter attributes most consistently associated with positive visitor outcomes were the interpreter's apparent degree of confidence and expression authentic emotion. The results can be used to inform interpretive training throughout the National Park Service.