Over the past several decades, the materials that we use to build medical devices and drug delivery systems have advanced dramatically, leading to new treatments for human disease. Here we will discuss materials that have been developed to deliver drugs inside of our cells. These synthetic nanoparticulate drug delivery systems have opened the door to new types of genetic therapies for the prevention, treatment, or even curing of human diseases. Perhaps the most famous examples today are the nanoparticles made from lipids and mRNA as vaccines for COVID. However, vaccines represent only a small part of the broad potential use of nanoparticles and RNA as therapeutics. We will describe the development and use of these technologies, as well as their potential as therapies for a range of different diseases.