Just over a century ago Max Planck introduced the quantized energy exchange between electromagnetic field modes in an optical cavity and the atoms comprising the walls at finite temperature to derive the spectral energy density of black body emission. Shortly thereafter, Einstein proposed that not only was the energy exchanged between the field and matter quantized, but that the radiation itself was quantized. He proposed that each light quantum, now called a photon, carries energy that is proportional to the frequency of the optical field mode. The frequency of a single photon is a central property that defines its physical state. Indeed, the full quantum state of a single photon is directly related to the electromagnetic field mode function that it occupies. Thus, we see that the central frequency of a single photon, often thought of as a defining property of a single light quantum, is not immutable, but can be modified just as the classical frequency of light can be manipulated. Here, we report the first experimental demonstration of deterministic spectral manipulation of single photons achieved by application of controlled spectral and temporal phases. These techniques lay the ground for future quantum wavelength- and time-division multiplexing applications and facilitate interfacing of different physical platforms where quantum information can be stored and manipulated.