Magnetite has wide applications in the fields of environment, biomedicine, and energy storage. Understanding the crystallization process of magnetite will improve the design and control of its properties. However, the challenge lies in determining the crystallization pathway of magnetite due to its nanosized and unstable intermediates. Recent developments in the in situ characterization techniques have shed light on this process, which has rarely been elucidated systematically. This review builds the correlation between the typical synthesis methods and the corresponding properties of magnetite. It also outlines a general multistage crystallization pathway involving a series of intermediates and explains how various strategies (e.g., pH and additives) modulate magnetite properties by influencing its intermediates during crystallization. To better illustrate published observations and reconcile conflicting perspectives, classical and state-of-the-art crystallization theories will be incorporated into each aspect. Moreover, this review highlights the importance of in situ characterization techniques, which enables the precise observation of crystallization processes. The goal of this review is to provide a fundamental understanding of magnetite crystallization and to guide the bottom-up design of magnetic materials for diverse applications.