Clinical laboratory science consists of various specialties such as clinical chemistry, hematology, immunology, microbiology, serology, toxicology, and urinalysis. This learning guide focuses on the major specialty of clinical chemistry, which encompasses a wide variety of tests and is a major area of concentration in hospital and reference core laboratories. Clinical chemistry uses many different methodologies, manual and fully automated tests, examines both very common and esoteric analytes, mixes basic chemistry with biochemistry, engineering, informatics, and other disciplines, and overlaps with other areas of concentration, in particular, toxicology and endocrinology.