Theoretically, transmission electron microscopy (TEM) is compatible with three different types of phase plate: thin-film, electrostatic, and magnetic. However, designing functional phase plates has been an arduous process that has suffered from unavoidable technical obstacles such as phase-plate charging and difficulties associated with micro-fabrication of electrostatic and magnetic phase plates. This review discusses phase-contrast schemes that allow visualization of transparent objects with high contrast. Next it deals with recent studies on biological applications ranging from proteins and viruses to whole cells. Finally, future prospects for overcoming the problem of phase-plate charging and for designing the next generation of phase-plates to solve the problem of electron loss inherent in thin-film phase plates are discussed.