Researchers have long relied on cited references in published research as pointers to the original published source of information. Citation indexes help researchers follow an idea backward and forward in time through the published literature.
Citation indexes are also used in citation analysis which collects data to determine the popularity and impact of research articles, researchers, and journals. Citation analysis is also used in the promotion and tenure process to assess the impact of individual faculty members' published articles. You can use citation indexes to locate when and where scholarly research has referenced your own published research.
There is no one single citation database that can be used to trace every use of an article or book. Citation indexes focus on scholarly publications and are heavily weighted to science and medicine. Non-English language sources are not extensively covered. There is much discussion in the scholarly community regarding these biases and how they influence journal rankings, academic department rankings, and tenure processes.
Sources for Citation Indexing
Google Scholar is a web search engine that searches peer-reviewed papers, theses, books, abstracts, and articles from academic publishers, professional societies, preprint repositories, universities, and other scholarly organizations. The number of times a piece has been cited in other scholarly literature is a factor in the rankings of Google Scholar results.
Below is a Google Scholar example, note that the number of times cited is hyperlinked, allowing the researcher to link to citing sources.