In　this　article,　the　invertible　matrices　over　commutative　semirings　are　studied.　Some　properties　and　equivalent　descriptions　of　the　invertible　matrices　are　given　and　the　inverse　matrix　of　an　invertible　matrix　is　presented　by　analogues　of　the　classic　adjoint　matrix.　Also,　Cramer＇s　rule　over　a　commutative　semiring　is　established.　The　main　results　obtained　in　this　article　generalize　the　corresponding　results　for　matrices　over　commutative　rings,　for　lattice　matrices,　for　incline　matrices,　for　matrices　over　zerosumfree　semirings　and　for　matrices　over　additively　regular　semirings.