In this paper, Matlis injective modules are introduced and studied. It is shown that every R-module has a (special) Matlis injective preenvelope over any ring R and every right R-module has a Matlis injective envelope when R is a right Noetherian ring. Moreover, it is shown that every right R-module has an ${mathcal{F}}^{{perp}1}$-envelope when R is a right Noetherian ring and $mathcal{F}$ is a class of injective right R-modules.