His work is the culmination of the noble line of research begun by Chebyshev, Stieltjes, Sergei Bernstein and Markov and continued by F Riesz, Banach and Szego . Krein brought the full force of mathematical analysis to bear on problems of function theory, operator theory, probability and mathematical physics.
Kanyang trabaho ay ang paghantong ng marangal na linya ng pananaliksik na sinimulan sa pamamagitan ng Chebyshev, Stieltjes, Daisy Bernstein at Markov at patuloy sa pamamagitan ng F Riesz, Banach at Szego. Krein nagdala ng buong lakas ng matematikal na pagsusuri upang madala sa mga problema ng mga function ng teorya, operator ng teorya, probabilidad at matematika physics.