The principal decay data for 64Cu were determined by 4πβ(PC)-γ coincidence techniques and photon spectrometry. The probability of electron capture was assessed from consistent results of three experiments; (1) measurements by the slope-to-intercept ratio method based on the 4π x-γ coincidence counting gated with the 1.34 MeV γ-rays, (2) K x-ray measurements with a calibrated low energy photon spectrometer (LEPS), and (3) 4π β-ray emission rate measurements using sandwiched sources. Method (1) is practically independent of the decay parameters. The emission rate per decay of the positrons decay and of the 1.34 MeV γ-rays were measured with a calibrated Ge γ-ray spectrometer. From these measurements, the branching fractions of positron decay, negatron decay and electron capture and the γ-intensity per decay could be evaluated with uncertainties between 1.0 and 1.2% except for about a 4% uncertainty for the γ fraction.