A police officer must be familiar with the latest scientific and technical developments in his profession, in addition to possessing at least some knowledge of criminal psychology and crime patterns. He must be aware of differences between one-time offenders and recidivists and of the reasons for crime increases, such as the institution of trial by jury. Jurors are deemed to be sentimentalists, ready to acquit recidivist criminals under the misapprehension of helping mankind, while actually such attitudes compound social problems. A complex crime form is prostitution with its attendant evils of pimping and white slavery, which in turn cause the social and medical problems of venereal diseases, especially syphillis. Police officers must know the classification of crimes against persons and property and be wise to sophisticated, high-class criminal professionals as well as to small-time, low-class delinquents. Police officers should be aware of the methods peculiar to each crime type and where criminals are likelky to congregate and ply their trade. Robbery, blackmail, mugging (the latter victimizing especially women to steal jewels and other valuables) are frequent, almost routine crimes, while other types of theft are more difficult to handle (e.g., thefts perpetrated by stage magicians turned pickpockets). In the area of criminalistics, a police officer must be skilled in crime science searches; evidence collection, preservation, and analysis; fingerprinting; police laboratory techniques; and use of photography in crime scene investigations. Finally, a police officer must strive for the highest professional and ethical standards in his work, while remembering that no one, even the most famous detective, is infallible. The text has neither footnotes nor appended references.