Genomic medicine is an evolving medical specialty that uses genomic information about an individual as part of their clinical care (e.g. for diagnostic or therapeutic decision-making). It has rapidly grown since the completion of the Human Genome Project in 2003. In England, the National Health Service's Genomic Medicine Service is considered to be the first national healthcare system to offer whole-genome sequencing as part of routine clinical care. Already, genomic medicine is making an impact in the fields of oncology, pharmacology, rare and undiagnosed diseases, infectious disease and neurology. In this article, we present a useful tool kit for clinicians working with individuals with intellectual disability, autism spectrum disorder and epilepsy. This article provides evidence for the importance of genetic testing, conveys an understanding of the range of genetic tests available and their diagnostic yields and how these apply to intellectual disability, autism spectrum disorder and epilepsy. Our simple tool kit gives information on when to refer to a clinical geneticist and where to find resources for clinicians and parents on genetic testing.