Increasingly, advanced information technologies affect both activity and travel participation. Although several studies have focused on specific activities such as e-shopping or telecommuting, this study focuses on the relationship between physical and virtual activity participation in maintenance and discretionary activities (specifically using Internet technologies). In particular, three related dimensions are investigated using a series of statistical models: (a) factors affecting information and communications technology (ICT) use and the propensity to perform virtual activities using the Internet, (b) the relationship between physical and virtual activity participation and ICT use, and (c) interactions among ICT use, activity attributes, and observed travel behavior. The models are estimated by using recent empirical activity-diary data from the San Francisco Bay Area (California). The results provide considerable evidence in support of substitution and generation of trips due to ICT use (particularly the Internet). The results highlight the influence of technological familiarity, work-related attributes, time constraints, timing of travel, mobility and connectivity needs, and sociodemographic factors on the interactions between ICT use and travel patterns of users. These results have important implications for travel demand estimation and forecasting given the growing adoption and use of ICT among various segments of the population.