  Animated avatars, which look and talk like humans, are iconic visions of the
future of AI-powered systems. Through many sci-fi movies we are acquainted with
the idea of speaking to such virtual personalities as if they were humans.
Today, we talk more and more to machines like Apple's Siri, e.g., to ask them
for the weather forecast. However, when asked for recommendations, e.g., for a
restaurant to go to, the limitations of such devices quickly become obvious.
They do not engage in a conversation to find out what we might prefer, they
often do not provide explanations for what they recommend, and they may have
difficulties remembering what was said one minute earlier. Conversational
recommender systems promise to address these limitations. In this paper, we
review existing approaches to build such systems, which developments we observe
today, which challenges are still open and why the development of
conversational recommenders represents one of the next grand challenges of AI.
