The impact of molecular (nucleic acid-based) methods on the basic science of medical microbiology is undeniable. Indeed, microbiologists have been at the forefront of the molecular biology revolution that has had such a dramatic effect on our understanding of biological science. Although the foregoing is indisputable, have these techniques yet found an appropriate, cost-effective, and quality-assured place in the clinical bacteriology laboratory? Are patients and the infections from which they may be suffering managed more effectively and efficiently through the application of molecular methods? This introduction seeks to explore these issues from the perspective of a clinical bacteriologist. Detailed theoretical and practical guidance on the application of these techniques to the diagnosis, management, and epidemiology of a wide range of infections is provided in the succeeding chapters.