This talk outlines Steady-state ab initio laser theory (SALT), a recently developed method for finding the steady-state solutions of the semiclassical laser equations directly without integrating them in time. The method approaches lasers as kind of non-hermitian scattering problem and is well-suited to deal with complex modern laser systems such as micro and nano lasers, photonic crystal and random lasers. The theory treats the openness of the cavity exactly and the non-linear modal interactions to infinite order; and has been shown to be very accurate for N-level lasers, even for multimode lasing high above threshold, in a large parameter regime. Two efficient techniques for solving these equations are briefly reviewed. The laser linewidth, a quantum property of the laser, can also be calculated via SALT based methods, leading to a general formula for the linewidth which contains all known corrections to the Schawlow-Townes formula (e.g. Petermann, Henry alpha) in limiting cases.