The Mathematics Subject Classification (MSC) is an alphanumerical classification scheme formulated by the American Mathematical Society based on the coverage of two major reviewing databases Mathematical Reviews and Zentralblatt MATH. It is used by many mathematics journals, which ask authors of research papers and expository articles to list subject codes from the Mathematics Subject Classification in their papers.
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The MSC is a hierarchical scheme, with three levels of structure. A classification can be two, three or five digits long, depending on how many levels of the classification scheme are used.
The first level is represented by a two digit number, the second by a letter, and the third by another two digit number. For example:
At the top level 64 mathematical disciplines are labeled with a unique 2 digit number. As well as the typical areas of mathematical research, there are top level categories for "History and Biography", "Mathematics Education", and for the overlap with different sciences. Physics is particularly well represented in the classification scheme with a number of different categories including:
All valid MSC classification codes must have at least the first level identifier.
The second level codes are a single letter from the Latin alphabet. These represent specific areas covered by the first level discipline. The second level codes vary from discipline to discipline.
For example, for Differential Geometry the top level code is 53, and the second level codes are:
In addition the special second level code "" is used for specific kinds of materials. These codes are of the form:
The second and third level of these codes are always the same  only the first level changes. It is not valid to put 53 as a classification, either 53 on its own, or better yet a more specific code should be used.
Third level codes are the most specific, usually corresponding to a specific kind of mathematical object or a well known problem or research area.
The third level code 99 exists in every category and means none of the above, but in this section
The AMS recommends that papers submitted to its journals for publication have one primary classification and one or more optional secondary classifications. A typical MSC subject class line on a research paper looks like
MSC Primary 03C90; Secondary 0302;
For papers on physics the Physics and Astronomy Classification Scheme is used instead. Due to the large overlap between Mathematics and Physics research is it quite common to see both PACS and MSC codes on research papers, particularly for multidisciplinary journals and repositories such as the arXiv.
The ACM Computing Classification System is a similar hierarchical classification scheme for Computer Science. There is some overlap between the AMS and ACM classification schemes, in subjects related to both mathematics and computer science, however the two schemes differ in the details of their organization of those topics.
The classification scheme used on the arXiv is chosen to reflect the papers submitted. As arXiv is multidisciplinary its classification scheme does not fit entirely with the MSC, ACM or PACS classification schemes. It is common to see codes from one or more of these schemes on individual papers.
The Mathematics Subject Classification (MSC) system is an alphanumeric ordering system for categorizing or arranging mathematical topics, similar to how a library arranges or orders their books on the shelves. The system was invented by the American Mathematical Society based on two major mathematical publishers: Mathematical Reviews and Zentralblatt MATH. The MSC system is used by many journals of mathematics which ask authors to list the MSC subject codes in their papers when submitted for publication. ^{[1]}
