The possiblity of observing gravitational waves produced in phase transitions the early Universe has greatly increased interest in BSM physics scenarios which feature a first order phase transition. Observing gravitational waves of cosmological origin is a part of the LISA (Laser Interferometer Space Antenna) gravitational wave space mission. In this talk I describe how phase transitions can be studied using an effective theory approach on the lattice, fully preserving the essential non-perturbative infrared physics. In particular I describe the analysis of a phase transition in 2-Higgs doublet model.
