Sample or specimen collection is an important and integral part of clinical biochemistry. Errors during collection, processing and transport of biological specimens are common causes leading to faulty result. So, utmost care should be taken to collect the sample in correct vials in proper condition. Some common sites of collection or sources of samples, urine preservatives, and hemolysis are also discussed in this chapter. The preservatives are primarily used as antimicrobial agent. The commonly used urine preservatives are formaldehyde, toluene, methanol, chloroform, thymol, etc.