  Novel data sources bring new opportunities to improve the quality of
recommender systems. Impressions are a novel data source containing past
recommendations (shown items) and traditional interactions. Researchers may use
impressions to refine user preferences and overcome the current limitations in
recommender systems research. The relevance and interest of impressions have
increased over the years; hence, the need for a review of relevant work on this
type of recommenders. We present a systematic literature review on recommender
systems using impressions, focusing on three fundamental angles in research:
recommenders, datasets, and evaluation methodologies. We provide three
categorizations of papers describing recommenders using impressions, present
each reviewed paper in detail, describe datasets with impressions, and analyze
the existing evaluation methodologies. Lastly, we present open questions and
future directions of interest, highlighting aspects missing in the literature
that can be addressed in future works.
