The development of Preimplantation Genetic Testing (PGT) is evolving fast, and best practice advice is essential for regulation and the development of new papers outlining recommendations for good practice in PGT was necessary. Background: Preimplantation genetic testing (PGT) is widely used today in In-vitro Fertilization (IVF) centers over the world for selecting euploid embryos for transfer and to improve clinical outcomes in terms of embryo implantation, clinical pregnancy, and live birth rates. Methods: We report the current knowledge concerning these procedures and the results from different clinical indications in which PGT is commonly applied. Biopsies for PGT. Finally, genetic and clinical significance of embryo mosaicism are illustrated. Preimplantation Genetic Testing for Aneuploidies (PGT-A) may be limited to women of advanced maternal age or with recurrent pregnancy loss, the fluid taken at the time of embryo biopsy can be analysed for any frozen embryo as well as PGT-A embryos. The current paper provides recommendations on the technical aspects of embryo biopsy and covers recommendations on the biopsy procedure, cryopreservation and laboratory issues and training, in addition to technical aspects and strengths and limitations specific for currently used techniques at different stages (polar body, cleavage stage and blastocyst biopsy).