Polygraph examination is considered by many a silver bullet, which is capable of revealing the truth although some are more sceptical regarding its usage. According to common belief polygraph examinations are easy to manipulate. What is the truth in connection with instrumental lie detection? How can it help the work of investigative authorities and the court? What are the dangers? The author not only gives answers to these questions but illustrates the work of examiners by real criminal cases, reviews the practice in different countries and gives an outline of the results of technical development as well. The author examines the critical remarks concerning instrumental lie detection, illuminates the weak points and makes his criminal-tactical recommendations. He enumerates the possibilities of polygraph examinations and illustrates their role in successful investigations in real cases.