Detailed mapping of the distributions and kinematics of gases in cometary comae at radio wavelengths can provide fundamental advances in our understanding of cometary activity and outgassing mechanisms. Furthermore, the measurement of molecular abundances in comets provides new insights into the chemical composition of some of the Solar Systems oldest and most primitive materials. Here we investigate the opportunities for significant progress in cometary science using a very large radio interferometer. The ngVLA concept will enable detection and mapping of a range of key coma species in the 1.2-116 GHz range, and will allow for the first time, high-resolution mapping of the fundamental cometary molecules OH and NH$_3$. The extremely high angular resolution and continuum sensitivity of the proposed ngVLA will also allow the possibility of imaging thermal emission from the nucleus itself, as well as large dust/ice grains in the comae, of comets passing within $sim1$ au of Earth.
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