Marcel Riesz (1886-1969) was the younger of the famed pair of mathematicians and brothers. Although Hungarian he spent most of his professional life in Sweden. He worked on summability theory, analytic functions, the moment problem, harmonic and functional analysis, potential theory and the wave equation. The depth of his research and the clarity of his writing place his work on the same level as that of his brother Frédéric Riesz. This edition of his Collected Papers contains most of Marcel Riesz's published papers with the exception of a few papers in Hungarian that were subsumed into later books. It also includes a translation by J. Horváth of Riesz's thesis on summable trigonometric series and summable power series. They are thus a valuable reference work for libraries and for researchers.