Results of a study on the planning of social activities are reported. Data collected in the Netherlands from social interaction diaries were used to estimate a multinomial logistic regression model to analyze whether a social activity is prearranged, routine, or spontaneous as a function of personal and household characteristics, social activity characteristics, and characteristics of the contacted person. The results show that the planning of social activities is significantly influenced by gender, presence of children, education level, income, and time spent on work and school. Social activity characteristics were also found to have a significant effect. Social activities scheduled later in the day are less likely to be routine. In contrast, social activities of longer duration and taking place on the weekend are more likely to be routine or planned. The location, the main purpose of the social interaction, and detailed characteristics of with whom the social interaction took place were also found to affect the scheduling process significantly.