Cesium hydrogen L-malate monohydrate, CsH(C4H4O5).H2O, is a new non-linear optical semi-organic crystalline material with a second harmonic generation efficiency roughly 2.5 times greater than KDP. Its crystal structure, space group P21, shows that the malate anions, are interconnected through directional O-H•••O hydrogen bonding, in a head-to-tail arrangement, creating extended anionic layers. The water molecules provide a cross-link, through hydrogen bonding, between adjacent layers. Especially noteworthy is that the Cesium cations and the COO- group from the malate anions, form a sequence of nearly perfectly aligned dipoles oriented along the b crystallographic axis giving a permanent dipole moment of 38 Debye per unit cell. As the crystals are non hygroscopic and easy to grow, they are potential new material for nonlinear optical and pyroelectric applications.