Measurements of third harmonic electron cyclotron emission have been made on the Advanced Toroidal Facility (ATF). Electron temperatures have been extracted from third harmonic, optically thin, electron cyclotron emission (ECE) measurements. The radial and temporal evolutions of the electron temperature have been characterized for electron cyclotron resonance heated discharges and for the early stages of neutral beam heated plasmas. A slab based emission model incorporating the equation of radiation transfer and ray tracing has been used to calculate the expected ECE. The results have been compared with experimental measurements. Measurements of the polarization of the third harmonic ECE during 1 T discharges have been compared with theoretical calculations of wave polarization rotation due to magnetic shear. Significant polarization of the emission was observed, and correction factors for a given wave frequency and peak density were obtained