There are two stackexchange sites that seem to have a bit of overlap: CS and CSTheory. CS states that it is for: "programming language semantics, formal methods ... or any other topic in theoretical or applied computer science at any level." where CSTheory is for "Specific research-level questions in theoretical computer science"

Does this mean that the difference is that CS is more geared towards questions that have a known answer, whereas CSTheory is for research only questions? For example, "What is the fastest known unification algorithm?" would go on CS while "Can unification algorithm X be made more efficient by Y?" would go on CSTheory?

Or do the two domains simply overlap?

  • $\begingroup$ its a long and tangled history under constant revision, and not necessarily explainable in words. dont overthink it too much. note that there are quite a few members that overlap incl many high-rep ones. also, charters/guidelines/scope are one thing, actual content/voting is another. one good strategy is just to look at the high-voted questions on each to see the difference & get feel for flavor. $\endgroup$
    – vzn
    Sep 23, 2013 at 20:20

2 Answers 2


In general, the difference between the two sites is one of breadth and level.

Breadth: the CS site covers questions in all areas of computer science. CSTheory is devoted to questions in theoretical computer science.

Level: This is the more crucial distinction. Questions in CSTheory are typically at the "grad student or higher level". As a quick rule of thumb, if the answer can be found in a textbook or by relatively straightforward googling, then CSTheory is NOT the place for it. If the right answer to a question is of the form "look in this lemma of this paper", then it's probably at the right level for CSTheory.

In your example, while I'm not sure what unification is (are you referring to the term from logic?), either question could be in scope for CSTheory if (say) it's not well known what the best algorithm is, or if there are subtleties in the definition of "fastest known" that require some expertise to tease out.


In addition to what Suresh wrote, keep in mind that the audiences are also different. The cstheory community is mainly composed of professional researchers in theoretical computer science. We have more specialists here who might not visit CS.SE. However the expectations from questions are also higher.

See also

  1. How to write a good question
  2. Is my question suitable for cstheory?

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