Active matter typically transforms chemical energy into motion at the local, microscopic scale. Examples of active matter range from molecular motors to swimming bacteria and self-propelling colloids. In this talk, I will focus on collective active motion that emerges from non-reciprocal interactions between particles of two different types. This is a basic model of the formation and self-propulsion of active colloids based on attractive-repulsive interaction forces between two types of otherwise non-motile microspheres. I will further show how we use field theory to calculate the entropy production of this non-equilibrium system.