Introduction: Karyotyping is the traditional method to detect the genetic mutation. Perhaps it has some limitations like tedi ous, low resolutions of results and strenuous. The fluorescence in situ hybridization technique brings a new era in molecular biology which is based on the complementary Deoxyribonucleic acid or Deoxyribonucleic acid/Ribonucleic acid strands. It is a combined approach of molecular and cytological to study chromosome structure and function as well as to detect the specific genes sequences. Objectives: To explore more knowledge about applications and different types of FISH. Due to the accuracy and versatility of FISH, it is widely used in cancer research to detect the various types of mutations, diagnostic and research fields. In this article, we briefly introduced MFISH (Multicolour FISH), QFISH (QuantitativeFISH) and RNA FISH. Method: The first step is to make short sequences of single-stranded DNA that should match a portion of the gene that is of interest. Now the tissue should be fixed by different fixers. Before hybridization, probes and sample sequences are denatured. To detect hybridized probes, different techniques are used. Result: As probes are labelled with different reporters, they can be detected by conventional light microscopy, fluorescence microscopy, etc. Conclusion: FISH and its types have a wide range of applications in the diagnostic field, genetic research, biomarker research and personalized medicines.