Poor immunogenicity remains the single biggest obstacle to human DNA vaccines achieving their potential. Strategies to improve DNA vaccine efficacy include codon optimization, transfection reagents, electroporation, vaccine adjuvants or combination with a protein or vector boost. Increased understanding of molecular events driving innate and adaptive immune responses has assisted development of molecular adjuvants for DNA vaccine use. Such adjuvants comprise plasmid-encoded signalling molecules including cytokines, chemokines, immune costimulatory molecules, toll-like receptor agonists or inhibitors of immune suppressive pathways. New approaches including gene knockdown, epigenetics and systems biology have also contributed to an increased range of molecular adjuvant options. This review explores current and future trends in vaccine design including the latest molecular adjuvants for enhanced DNA vaccine efficacy.