We propose a general framework for the study of L1 contractive semigroups of solutions to conservation laws with discontinuous flux: ut + f(x, u)x = 0, f(x, u) = ( f (u), x < 0, f(u), x > 0, (CL) where the fluxes f , f are mainly assumed to be continuous. Developing the ideas of a number of preceding works (Baiti and Jenssen [14], Audusse and Perthame [12], Garavello et al. [35], Adimurthi et a...