Two studies tested littering norm activation by trash can design. The first was a scenario study using a 4 (norm type: social injunctive vs. social descriptive vs. personal vs. control) x 2 (activation type: explicit vs. implicit activation) between-group design, with judgments of a litterer as the dependent variable. Explicit norm activation was more effective than implicit activation. A field study subsequently tested the effect of personal norm activation on actual littering behavior, following a 2 (explicit activation: no vs. yes) x 2 (Implicit activation: no vs. yes) between-group design. Here, both explicit activation through a verbal prompt and implicit activation through design had significant effects, reducing the amount of litter by 50%. A post hoc survey revealed significant effects of age and gender on the personal norm against littering. These findings helped explain the absence of norm activation effects in the youngest age group as found in the field study.