Reduction was once a central topic in philosophy of science. I claim that it remains important, especially when applied to problems and problem-solutions rather than only to large theory-complexes. Without attempting a comprehensive classification, I discuss various kinds of problem reductions and similar relations, illustrating them, inter alia, in terms of the blackbook-body problem and early quantization problems. Kuhn’s early work is suggestive here both for structuralist theory of science and for the line I prefer to take. My central claims in the paper are (1) that problem reduction is important in its own right and does not “reduce” to theory reduction and (2) that problem reduction is generally more important than theory reduction to methodology as the “control theory” of inquiry.