Cosmological first order phase transitions are a promising source of gravitational waves, and a possible explanation of the baryon asymmetry and dark matter abundance. Predicting the phenomenological consequences of such phase transitions requires knowledge of the expansion velocity of the bubbles formed in a phase transition. In this talk, I will present WallGo, a software package for the computation of bubble wall velocities. WallGo is the first publicly available code that computes the matrix elements, collision integrals Boltzmann equation and scalar field equation of motion for user-defined models. I will present results obtained with WallGo, and discuss its limitations. Lastly, I will discuss several simplifying regimes in the computation of the wall velocity, such as the ballistic limit and a large jump in degrees of freedom.