In this contribution, a mm-wave all-dielectric linearto-circular polarization converter is reported for the first time. The proposed converter consists of a periodic stack of isotropic dielectric substrates that produces form birefringence. By virtue of the anisotropy of the permittivity tensor, the phase-shift introduced between two orthogonally linearly polarized transmitted electromagnetic waves can be controlled, enabling linear to circular polarization conversion. Due to its all-dielectric nature, the proposed polarization converter circumvents oxidation, corrosion and power handling problems associated with metallic structures. Our measurements demonstrate 17% 1dB axial ratio fractional bandwidth and 39% below 3dB, while measured insertion loss is 0.6dB at the operating frequency. The proposed polarization converter further benefits from angularly stable response up to 40 degrees.