Piezoelectric polymer has several unique properties compared with conventional piezoelectric materials, namely (1) low acoustic impedance, (2) high flexibility, (3) a relatively low dielectric constant, (4) high breakdown voltage, (5) resistance mechanical and thermal shock. A thin sheet of wide area can be easily produced, and it can be properly given local piezoactivity. At the present stage, polarized stretched films of polyvinylidene fluoride (PVDF) are considered to be most promising in practical use. Various transducers with PVDF films have been developed in the field of acoustics from audio engineering to ultrasonics, such as microphones, headphones, loudspeakers, electromechanical transformers, ultrasonic transducers, and so on. Principles and constructions of these transducers especially for ultrasonics are described including several new constructions which have been recently proposed. Applications of these transducers to electronic devices as well as ultrasonic imaging systems are also described.