Conversational agents โ€“ technologies that communicate with their users via natural language โ€“ are widely implemented by (commercial) organizations. They are seen as a promising way to communicate (branded) content to users and allow for new types of consumer-brand interactions. Due to their conversational nature and possibly including more hidden types of advertising, conversational agents can potentially influence its users in more effective ways than other types of online media. This dissertation provides insights into (1) the persuasive consequences following from interactions with conversational agents in a brand communication context, (2) the possible underlying mechanisms explaining these effects, and (3) the short- and long-term dynamics of these effects. This dissertation shows that conversational agents have largely the same effects on affective, cognitive, and behavioral persuasive outcomes as interactive websites; and different agent forms also influence these outcomes to a similar extent. Several underlying mechanisms related to the communication entity (i.e., human-likeness, privacy concerns, trust) and the interaction (i.e., enjoyment, perceived interactivity, cognitive load) can explain the persuasiveness of conversational agents. Affective and behavioral persuasive outcomes as well as trust in conversational agents remain relatively stable over time. In sum, up to this date, conversational agents do not fully live up to their persuasive potential yet, but under certain circumstances they can be persuasive agents by influencing how users feel about, think about and act towards them, the messages they provide, and brands being advertised in their messages.