Using expectancy theory, this study aimed at identifying the attitudinal/behavioral factors that explain the relationship between Internet expectancies and Internet addiction among Taiwanese adolescents. A total of 25,573 students (49.8% boys and 50.2% girls) across junior and senior high schools participated in the study. The students reported on their background characteristics, general expectations from the Internet, attitudes toward online social interaction and online gaming, preferences in online social interaction, and dys-controlled online gaming behavior. Structural equation modeling was used to examine the indirect effects of Internet expectancies on Internet addiction through these attitudinal/behavioral factors. The results showed that Internet expectancies positively predicted students' attitudes toward online games and online social interaction, which in turn predicted their respective preferences or dys-controlled behavior and Internet addiction. The indirect effect of Internet expectancies was higher on Internet addiction via attitudes toward online gaming and dys-controlled online gaming than via attitudes toward and preferences of online social interaction. The indirect effects exhibited a larger impact on boys than on girls. The authors recommend that the expectancies of online gaming and social interaction be addressed in efforts to prevent and attenuate the severity of adolescent Internet addiction.