Book excerpt: This book presents a clear and comprehensive review of the current status of three-dimensional (3D) digital holographic imaging of phase microscopic objects, with insightful discussions on the positive and negative features of classical, electronic and holographic microscopy. The technical details and results of the restoration of the 3D shapes of red blood cells, bacteria, yeasts, thin films and other micro-objects are presented. The physical background of the method was substantiated by the authors in 1989 and in 1998, the very first digital holographic interference microscope was developed. Clear evidence of the pathological flattened shape of the erythrocytes relevant to different pathologies is given by detailed measurements on the 3D images. Based on the model of the erythrocyte as a liquid-filled, charged, and viscoelastic shell reinforced by skeleton, numerical computations of the equilibrium shapes of human erythrocytes are made, and the results are analyzed and compared to the 3D visualization data.