Solid magnesium hydride MgH2∞ has been pursued as a potential hydrogen‐storage material. Organic chemists were rather interested in soluble magnesium hydride reagents from mid‐20th century. It was only in the last two decades that molecular magnesium hydride chemistry received a major boost from organometallic chemists with a series of structurally well‐characterized examples that continues to build a whole new class of compounds. More than 40 such species have been isolated, ranging from mononuclear terminal hydrides to large hydride clusters with more than 10 magnesium atoms. They provide not only insights into the structure and bonding of Mg−H motifs, but also serve as models for hydrogen‐storage materials. Some of them are also recognized to participate in catalytic transformations, such as hydroelementation. Herein, an overview of these molecular magnesium hydrides is given, focusing on their synthesis and structural characterization. Searching for the right size: Molecular magnesium hydrides, including larger clusters have been studied as potential hydrogen‐storage materials. An overview of structurally well‐defined molecular magnesium hydrides including larger clusters is compiled with emphasis on their synthesis, characterization, and properties.