Citation tracking, or citation analysis is an important tool used to trace scholarly research, measure impact, and inform tenure and funding decisions. The impact of an article is evaluated by counting the number of times other authors cite it in their work. Researchers do citation analysis for several reasons:

• find out how much impact a particular article has had, by showing which other authors have cited the article in their own paper
• find out how much impact a particular author has had by looking at the frequency and number of his/her total citations
• discover more about the development of a field or topic (by reading the papers that cite a seminal work in that area)

The output from citation studies is often the only way that non-specialists in governments and funding agencies, or even those in different scientific disciplines, can judge the importance of a piece of scientific research.

The best known article level metric is the number of times an article has been cited. Cameron Neylon explains why new article-level metrics are needed. Technology and Open Access have made other types of metrics possible. Other article metrics include counting:

• page views
• downloads
• mentions in blogs
• inclusions in social bookmarking tools.

PLoS pioneered many of these new article metrics. They provide a great overview of the topic. BioMed Central indicates "most viewed" and "highly cited" cited articles and allows readers to comment on articles.

The Social Science Research Network (SSRN), a repository of social science articles, counts article downloads and provides lists of top articles, authors, and institutions based on the download counts.

See Altmetrics for more information about newer measures.

Reviews and recommendations of articles are valuable to scholars. Some journals (like Computing Reviews) offer reviews of articles that appear in other journals. Journal clubs are popular because they allow a group to discuss an article in-depth. Now Web 2.0 and social networking tools allow readers to comment upon and rank articles.

Faculty of 1000 (or F1000) is the best-known service that provides recommendations, evaluations, and rankings of articles.

PubPeer creates a database of comments about published articles.

Many publishers now provide readers the ability to rate or comment on published articles. Some of these publishers are listed below.

• BioMed Central
• Frontiers
• Nature Publishing Group
• PLoS