A general description of the phenomena of ferroelectricity is given together with a brief history of the subject. A comparison is made between ferroelectricity and ferromagnetism.Next, a more detailed description is made of the properties of the three main types of ferroelectrics: the barium titanate, KDP (potassium dihydrogen phosphate), and Rochelle salttypes. Finally the electrical properties of these substances are discussed in relation to their crystal structures.