This article explores the complex ways in which the Internet affects interpersonal communication and sociability. Dynamic new time-diary data identify when and where Internet use impacts face-to-face interactions. Internet use at home has a strong negative impact on time spent with friends and family as well as time spent on social activities, but Internet use at work has no such effect. Similarly, Internet use during weekend days is more strongly related to decreased time spent with friends and family and on social activities than Internet use during weekdays.

These findings offer support for a "displacement" theory of Internet use -- time online is largely an asocial activity that competes with, rather than complements, face-to-face social time. However, it is the location and timing of Internet use that determines how interpersonal relationships are affected.

The Internet and other information technologies represent a significant departure from previous communication technologies by combining features of both interpersonal communication and mass communication. According to the "functional equivalence" argument that has been applied to the diffusion of earlier communication technologies, one should expect decreases in both types of communication activities as Internet use increases. An effective and comprehensive method for testing which activities are most affected by the Internet is through the 24-hour time-diary studies, in which all daily activity is recorded

When the time-diaries of Internet users and nonusers in a combined 1998-2001 national sample are compared, few consistent differences in the social lives of Internet users are found. This raises questions about whether the Internet acts more to enhance communication behaviors rather than to displace behavior -- which seems to be the case for television, as predicted by the functional equivalence hypothesis.

The ability of time-diary studies to document trade-offs in daily behavior is hampered by their focus on a single day's activities, since there is little time to capture the full range of activities that may result from engaging in any single activity (like IT usage) on a single day. The present study takes advantage of a year 2000 data collection involving a national sample of more than 400 working middle-class families, all of whose members kept a complete weekly account of all their activities. The sample has the additional advantage of being restricted to a relatively homogeneous population group in terms of age, family circumstance and life stage.

The major differences found between Internet users and nonusers in this study is in terms of the 4+ lower paid work hours of Internet users that offset their 4+ weekly hours of Internet use, which took place mainly at home (not at work). That meant that these Internet users did spend more time alone during the week, but not significantly more and not at the expense of contact with family members, relatives or friends. Otherwise the diary figures of Internet users and nonusers are strikingly similar.