A method for the assembly of a polynucleic acid from a plurality of nucleic acids in which the polynucleic acid is of a formula N n+1, in which N represents a nucleic acid and where n is 1 or greater than 1 and each N may be the same or a different nucleic acid, in which the method comprises: (i) providing a first nucleic acid N1 which has an oligonucleotide linker L1 3' attached by ligation at the 3'-end of the nucleic acid; (ii) providing a second nucleic acid N2 which optionally has an oligonucleotide linker L2 3' attached by ligation at the 3'-end of the nucleic acid and which has an oligonucleotide linker L2 5' attached by ligation at the 5'-end of the nucleic acid, wherein the 5'-end linker L2 5' of nucleic acid N2 is complementary to the 3'-end linker L1 3' of nucleic acid N1; (iii) optionally providing one or more additional nucleic acids N, wherein nucleic acid N2 has an oligonucleotide linker L2 3' attached by ligation at the 3'-end of the nucleic acid, and wherein said one or more additional nucleic acids N comprises a terminal additional nucleic acid NZ, and wherein each additional nucleic acid N has an oligonucleotide linker attached by ligation at its 3'-end, wherein said terminal additional nucleic acid NZ optionally lacks an oligonucleotide linker at its 3'-end and wherein each additional nucleic acid N has an oligonucleotide linker attached by ligation at its 5'-end, wherein for the first additional nucleic acid N3 the 5'-end linker L3 5' is complementary to the 3'-end linker L2 3' of nucleic acid N2 and for each second and subsequent additional nucleic acid N the 5'-end linker is complementary to the 3'-end linker of the respective preceding additional nucleic acid; and (iv) ligating said nucleic acids to form said polynucleic acid; wherein at least step (iv) is carried out on a microfluidic device. (i) providing a first nucleic acid N1 which has an oligonucleotide linker L1 3' attached by ligation at the 3'-end of the nucleic acid; (ii) providing a second nucleic acid N2 which optionally has an oligonucleotide linker L2 3' attached by ligation at the 3'-end of the nucleic acid and which has an oligonucleotide linker L2 5' attached by ligation at the 5'-end of the nucleic acid, wherein the 5'-end linker L2 5' of nucleic acid N2 is complementary to the 3'-end linker L1 3' of nucleic acid N1; (iii) optionally providing one or more additional nucleic acids N, wherein nucleic acid N2 has an oligonucleotide linker L2 3' attached by ligation at the 3'-end of the nucleic acid, and wherein said one or more additional nucleic acids N comprises a terminal additional nucleic acid NZ, and wherein each additional nucleic acid N has an oligonucleotide linker attached by ligation at its 3'-end, wherein said terminal additional nucleic acid NZ optionally lacks an oligonucleotide linker at its 3'-end and wherein each additional nucleic acid N has an oligonucleotide linker attached by ligation at its 5'-end, wherein for the first additional nucleic acid N3 the 5'-end linker L3 5' is complementary to the 3'-end linker L2 3' of nucleic acid N2 and for each second and subsequent additional nucleic acid N the 5'-end linker is complementary to the 3'-end linker of the respective preceding additional nucleic acid; and (iv) ligating said nucleic acids to form said polynucleic acid; wherein at least step (iv) is carried out on a microfluidic device.