Broadly speaking, academic literature can be classified into two types: original research and review articles. Original research constitutes the bulk of academic writing, namely papers that aim to make some new contribution (and often quite specialised and specific) contribution to the literature. Original research articles can be theoretical, empirical, or a combination of both, though usually they focus on one or the other. By contrast, review articles do not present any new insights or results that have not been published before. Rather, review articles attempt to summarise and synthesise the existing literature and findings about a particular question. Although they can vary in scope, they are typically much broader than original research articles, since they often aim to cover a range of approaches to answering a particular question. Research articles can often be less technical than original research papers as many methodological details and complications are typically omitted, and hence they tend to be more accessible to a general audience than original research articles. Since they summarise a range of research in a relatively more accessible form, review articles can serve as a very useful introduction into a particular field of research. They are especially useful for areas, for instance in public policy or medical studies, where different studies frequently yield conflicting results, as a good review article will compare and contrast the results across many studies and approaches, providing a broader picture of the evidence base as a whole.
Systematic reviews: additional information and discussion about the benefits and limitations of review articles from Sense About Science
Annual reviews: an academic publisher which publishes review articles in a wide range of fields