2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/52243We review a special class of semiclassical string states in AdS_5 x S^5 which have a regular expansion of their energy in integer powers of the ratio of the square of string tension (`t Hooft coupling) and the square of large angular momentum in S^5. They allow one to quantitatively check the AdS/CFT duality in non-supersymmetric sector of states and also help to uncover the role of integrable structures on the two sides of the string theory -- gauge theory duality.57 pages, latex. To appear in Ian Kogan Memorial Volume, ``From Fields to Strings: Circumnavigating Theoretical Physics'', M. Shifman, A. Vainshtein, and J. Wheater, eds. (World Scientific, 2004); v2: table of contents and references added; v3: minor misprints correctedHigh Energy Physics - Theorytext