Research into plant genetics often requires the suppression or complete knockout of gene expression to scientifically validate gene function. In addition, the phenotypes obtained from gene suppression can occasionally have commercial value for plant breeders. Until recently, the methodological choices to achieve these goals fell into two broad types: either some form of RNA-based gene silencing; or the screening of large numbers of natural or induced random genomic mutations. The more recent invention of gene editing as a tool for targeted mutation potentially gives researchers and plant breeders another route to block gene function. RNAi is widely used in animal and plant research and functions to silence gene expression by degrading the target gene transcript. Although RNAi offers unique advantages over genomic mutations, it often leads to the formation of a genetically modified organism (GMO), which for commercial activities has major regulatory and acceptance issues in some regions of the world. Traditional methods of generating genomic mutations are more laborious and uncertain to achieve the desired goals but possess a distinct advantage of not being governed by GMO regulations. Gene editing (GE) technologies have some of the advantages of both RNAi and classical mutation breeding in that they can be designed to give simple knockouts or to modulate gene expression more subtly. GE also has a more complex regulatory position, with some countries treating it as another conventional breeding method whilst the EU defines GE as a technique of genetic modification and applies the normal GMO authorization procedures. This chapter explores the pros and cons of RNAi alongside other methods of modulating gene function.