The invention relates to the use of specific terminal deoxynucleotidyl transferase (TdT) enzymes in a method of nucleic acid synthesis, to methods of synthesizing nucleic acids, and to the use of kits comprising said enzymes in a method of nucleic acid synthesis. The invention also relates to the use of terminal deoxynucleotidyl transferases and 3′-blocked nucleotide triphosphates in a method of template independent nucleic acid synthesis.