The use of various in vitro systems is expanding dramatically not only in basic research, but also to meet regulatory requirements for chemicals and products of various kinds. Further significant developments are certain to result from the use of in vitro systems for high-throughput screening in pharmacology and toxicology. Because the maintenance of high standards is fundamental to all good scientific practice and is essential for maximising the reproducibility, reliability, credibility, acceptance and proper application of any results produced, guidelines have been developed to define minimum standards in cell and tissue culture to be called as Good Cell Culture Practice (GCCP). The scope of this chapter has been broadly defined to include systems based on cells and tissues obtained from humans and animals, issues related to the characterisation and maintenance of essential characteristics, as well as quality assurance; recording and reporting; safety, education and training; and ethics. This GCCP guidance lists a set of six principles intended to support best practice in all aspects of the use of cells and tissues in vitro, and to complement, but not to replace, any existing guidance, guidelines or regulations.