Guido L. Weiss (born 29 December 1928 in Trieste) is an American mathematician, working in analysis, especially Fourier analysis and harmonic analysis.
Weiss studied at the University of Chicago, where he received in 1951 his master's degree and in 1956 under Antoni Zygmund his PhD with thesis On certain classes of function spaces and on the interpolation of sublinear operators. At DePaul University he became an instructor in 1955, an assistant professor in 1956, and in 1959 an associate professor. in 1960 he was a visiting professor in Buenos Aires and in the same year a postdoc at the Institut Henri Poincaré in Paris. In 1961 Weiss became an associate professor and in 1963 a professor at Washington University in St. Louis, where from 1967 to 1970 he was also chair of the mathematics department. He was a visiting professor at several universities, including the University of Geneva (1964–65), the Université Paris-Sud (1970–71), the Scuola Normale Superiore in Pisa (1980), in Madrid and in Beijing. In the academic year 1987–88 he was at MSRI as the organizer of a program in classical analysis.
In 1967 Weiss won the Chauvenet Prize for his book Harmonic Analysis. In 1994 he was given honorary doctorates in Milan and Barcelona. In 2012 he became a fellow of the American Mathematical Society.