AbstractA Code of Practice is prepared based on the comprehensive work within internal, national and international projects. The guidelines are established for specimen selection to be followed in experimental studies. The Code of Practice is prepared based on the authors' and project partners' long years of experience in the subject field of high temperature testing, deformation studies and creep crack growth on ferritic and austenitic materials, including C-Mn, P22, P91 and 316 steels and their weldments. FE calculations and validation tests were carried out on industrially relevant specimen geometries. The Code of Practice gives advice on testing, measurements and analysis of test data for a range of creep brittle to creep ductile materials tested using different specimen sizes and geometries. Along with guidelines of Code of Practice, validation test results are presented for the applicability of the Code of Practice to the selected materials and geometries.