The present chapter deals with matter-wave solitons of Bose-Einstein condensatesBose-Einstein condensate in spatial periodic potentials. TheBose-Einstein condensate mathematical models used in this chapter is the Gross-Pitaevskii equationsGross-Pitaevskii equation with either cubic nonlinearity or cubic and quintic nonlinearities with either a spatial or spatiotemporal periodic potential that model the dynamics of BECs in periodic potentials. Analytical exact soliton/solitary wave solutions of the considered GP equations are presented and then used for investigating analytically the dynamical properties of matter-wave solitons in the corresponding BEC systems. In some situations, numerical simulations are also carried out, especially on the stability of found matter-wave solitons.