A magnetic spiral-orbit spectrometer was used to study the positron spectrum from an isotropic μ+ decay. The detected positrons were identified by an electronic technique designed to measure the lifetime of the muon. Our measured weighted mean value of the μ+ mean life is τμ=2.21+/-0.02 μsec. The data have been analyzed according to the simplified one-parameter theory of Michel, as modified by Behrends, Finkelstein, and Sirlin and corrected by Berman to include radiative corrections to the muon decay theory. We obtained ρM=0.741+/-0.027 for the Michel parameter as the weighted mean value from four experiments. In these experiments the measurements in the low-energy positron region were not of sufficient accuracy to yield an estimate of the second Michel parameter. Included is a measurement of the maximum positron energy. The weighted mean value of this measurement is W=52.87+/-0.07 Mev. From this value and its simple algebraic relation to the masses of the decay particles one obtains a value of the μ+ mass μ=206.94+/-0.27. Tables of the radiative correction to muon decay are given as well as the total corrections that must be added to the Michel parameter that is derived from experimental data by using the simple Michel theory without radiative corrections. For the energy region of the majority of experiments from which the ρM value is determined, this total correction in ∆ρ is approximately 0.040. From our measured value of the maximum positron energy, an estimate is made of the possible upper limit on the mass of the neutral particle in muon decay. This upper limit is reported as 8 electron-mass units.