The presence of genotoxic agents in the environment may cause chromosomal mutations through different mechanisms, which are associated with serious health effects. Tests that help to determine irreversible genetic abnormalities and those that offer indirect proof of DNA damage are both included in genotoxicity testing, which are used to discover chemicals that affect genetic material. Since individual tests do not reveal all the end points, a panel of tests is typically thought to be the most thorough way to assess a chemical’s capacity to cause genotoxicity. A commonly used and well-known assay in genetic toxicology for determining the genotoxic potential of chemical substances, medications, and environmental variables are the in vivo micronucleus (MN) and chromosomal aberration (CA) test in bone marrow (BM). These in vivo cytogenetic tests use bone marrow of rodents to ascertain chemical damage to the chromosomes or mitotic apparatus of mammalian cells and examine via microscopy. An increase in the frequency of micronucleated polychromatic erythrocytes (MN PCEs) and aberrant chromosomes in treated animals is an indication of genotoxicity. This chapter offers a concise overview of the widely utilized fundamental tests and their protocols used for regulatory purposes.