This book gives a basic idea about the mutations, their types, and their consequences. It includes chromosomal mutations and gene mutations. In chromosomal mutation, the structural and numerical changes are explained. The chapter on changes in chromosome structure includes the deletion or deficiency mutation, duplication, inversion, and translocation with suitable examples. The probable mechanism of development of such changes is also briefly discussed. The behavior of aberrated chromosomes in cell division is included. The chapter on changes in chromosome number gives information about euploidy and aneuploidy, the mechanism, and suitable examples. The chapter on Gene mutations covers point mutation and frameshift mutation, and the causes and consequences of the mutations. A brief introduction to induced mutation is given in the last chapter. It discusses physical and chemical mutagenesis and targeted mutagenesis.