Molecules play a crucial role in all branches of astrophysics, particularly in the analysis of planetary and stellar spectra, as well as contributing to the all important envelope opacities needed for modelling the evolution of cool stars.  Until 2010, line positions and strengths for all astrophysically important molecules were sparse, and the ExoMol project was setup by Jonathan Tennyson and Sergey Yurchencko in 2011 to use state-of-the-art quantum mechanics to calculate the billions of line strengths and positions needed for all molecules of interest.  As well as describing the ExoMol project, I plan to discuss my own contribution, which involves the C3 molecule and its isotopologues.