This chapter examines deoxyribonucleic acid (DNA) identification, a technique used for over 30 years in criminal investigations. The use of DNA identification by law enforcement agencies continues to expand as new techniques are developed and technology enables it to be applied more efficiently. The chapter begins with an examination of the scientific and historical background of DNA identification. This is followed by a discussion of DNA databases, more recent techniques in this field and the application of DNA in criminal prosecutions. There have been many documented cases of police covertly obtaining evidence in an attempt to enhance criminal investigations. Further opportunities for obtaining DNA profiles include using blood obtained from mosquitoes or leeches to provide a DNA profile that can be used as evidence in a criminal trial. In order to be considered reasonable, a search needs to be supported by a warrant on the basis of 'probable cause': the reasonable belief that the individual has committed a crime.