This review provides a comprehensive overview of flux compactifications in string theory, focusing on closed string fluxes in type II theories. It begins by discussing supersymmetric flux configurations with maximally symmetric four-dimensional spaces and the no-go theorems for compactifications with fluxes, along with their evasion. The review then delves into the resulting four-dimensional effective theories, including perturbative and non-perturbative corrections, particularly focusing on moduli stabilization. Finally, it briefly touches on statistical studies of flux backgrounds. The paper is structured into several sections, covering basic definitions, supersymmetric backgrounds with fluxes, no-go theorems, effective theories, moduli stabilization, and distributions of flux vacua. It aims to provide a pedagogical exploration of the literature, discussing recent developments and focusing on type II compactifications with $\mathcal{N}=1$ supersymmetric flux vacua.This review provides a comprehensive overview of flux compactifications in string theory, focusing on closed string fluxes in type II theories. It begins by discussing supersymmetric flux configurations with maximally symmetric four-dimensional spaces and the no-go theorems for compactifications with fluxes, along with their evasion. The review then delves into the resulting four-dimensional effective theories, including perturbative and non-perturbative corrections, particularly focusing on moduli stabilization. Finally, it briefly touches on statistical studies of flux backgrounds. The paper is structured into several sections, covering basic definitions, supersymmetric backgrounds with fluxes, no-go theorems, effective theories, moduli stabilization, and distributions of flux vacua. It aims to provide a pedagogical exploration of the literature, discussing recent developments and focusing on type II compactifications with $\mathcal{N}=1$ supersymmetric flux vacua.