Developing software agents that users will trust with sensitive information is very difficult. There is a twice-removed relationship between the users and their tasks, and this remote interaction leads to significant concerns and interesting opportunities. A model of agent acceptance is proposed based on earlier work on user attitudes towards e-commerce transactions. This model describes how feelings of trust and perceptions of risk combine in opposite directions to determine a user's final acceptance of an agent technology. Specific factors that contribute to trust and risk are reviewed including experience, system performance, human-agent communication, interface design, and agent autonomy.