Abstract: Microcausality states that field operators commute at spacelike separations. While this property holds directly for Lorentz-invariant states, it becomes more subtle when Lorentz symmetry is spontaneously broken. In this talk, I analyze the operatorial commutator in interacting scalar field theories using the interaction picture formalism. For theories without derivative interactions, I show that microcausality is preserved, ensuring that the interacting commutator still vanishes outside the standard Minkowski light cone, regardless of the state considered. In contrast, derivative interactions modify the free-theory commutator by introducing corrections proportional to derivatives of delta functions, evaluated on the light cone of the free theory. When expectation values are taken, these corrections cancel in Lorentz-invariant states but persist in states where Lorentz symmetry is spontaneously broken. I show that these terms are the signal of a perturbative shift in the light-cone structure of the free theory, due to interactions. Finally, I discuss what goes wrong with the standard argument according to which Lorentz invariance implies microcausality.