Cohen, Boyer and associates developed the first practical method for cloning genes, by the formation of recombinant plasmids which can be used to infect plasmid-free bacteria. The authors demonstrated that if DNA is fragmented with restriction endonucleases and combined with similarly restricted plasmid DNA, the resulting recombinant DNA molecules are biologically active and can replicate in host bacterial cells. Plasmids can thus act as vectors for the propagation of foreign cloned genes. This paper is available from the PNAS at this link.

The method that Cohen and Boyer invented eventually resulted in U.S. patent No. 4,237,224 granted to Cohen and Boyer on December 2, 1980. This patent, "Process for producing biologically functional molecular chimeras," was the foundation of the biotechnology industry. 

Cohen published a semi-popular account of this research as "The manipulation of genes," Scientific American, 233 (1975) 24-33.

Creation of the first transgenic organism: expression of Staphylococcus aureus genes in Escherichia coli. Digital facsimile from pnas.org at this link.

Confirmation of the success of methods outlined in No. 257.5.
Abstract:
"Genes carried by EcoRI endonuclease-generated fragments of Staphylococcus plasmid DNA have been covalently joined to the E. coli antibiotic-resistance plasmid pSC101, and the resulting hybrid molecules have been introduced into E. coli by transformation. The newly constructed plasmids replicate as biologically functional units in E. coli, and express genetic information carried by both of the parent DNA molecules. In addition, electron microscope heteroduplex analysis of the recombinant plasmids indicate that they contain DNA sequences derived from E. coli and Staphylococcus aureus. Recombinant molecules can transform other E. coli cells for penicillin-resistance markers originally carried by the staphylococcal plasmid, and can be transferred among E. coli strains by conjugally proficient transfer plasmids."  Digital facsimile from PubMedCentral at this link.