Polyomaviruses are a group of small, non-enveloped viruses that belong to the family Polyomaviridae. They are known for their ability to infect a variety of hosts, including humans and animals. These viruses can remain dormant in the body and may reactivate under certain conditions, potentially leading to diseases, especially in individuals with weakened immune systems. One of the most studied human polyomaviruses is JC virus, which is associated with a serious neurological condition called progressive multifocal leukoencephalopathy (PML). Another notable example is BK virus, which can cause complications in kidney transplant patients. Understanding polyomaviruses is important for developing effective treatments and preventive measures.