Delivery of nucleic acids is the most promising therapy for many diseases that remain untreatable. Therefore, many research efforts have been put on finding a safe and efficient delivery system able to provide a sustained response. Viral vectors have proved to be the most efficient for delivery of nucleic acids and, thus, stand as the foremost vector used in current clinical trials. However, safety issues arise as a main concern and mitigate their use, impelling the improvement of non-viral alternatives. This review focuses on the recent advances in pre-clinical development of non-viral polyplexes and lipoplexes for nucleic acid-based delivery, in contrast with vectors being used in present clinical trials. Nucleic acid vectors for neurodegenerative ataxias, Parkinson's disease, retinitis pigmentosa, cystic fibrosis, hemophilia, pancreatic and lung cancer, and rheumatoid arthritis are discussed to illustrate current state of pre-clinical and clinical studies. Thereby, denoting the prospects for treatment of genetic diseases and elucidating the trend in non-viral vector development and improvement which is expected to significantly increase disease rescue exceeding the modest clinical successes observed so far.