Identification of organisms has become important to preserve species because of increasing habitat destruction. We know very less about diversity of plants and animals that are living on earth. There is estimation of 5 to 50 million plants and animal species out of which less than 2 million have been identified. Yearly rate of extinction has increases from one species per million to 100’1,000 species per million which means thousand of plants and animals are lost each year, most of which are not identifies yet.  The high levels of destruction and endangerment of ecosystem has lead to improved system for identifying species. In recent years a new ecological (preservation) approach called DNA barcoding has been proposed to identify species and ecology research.   DNA barcoding is a system for fast and accurate species identification which will make ecological system more accessible. 
DNA barcoding first came to attention of the scientific community in 2003 when Paul Hebert’s science research group at university of Guelph published a paper titled ‘biological identifications through DNA bar codes’. DNA barcoding is tool for identification of species and for taxonomic research. DNA barcoding is not a new concept as Carl Woese used rRNA and molecular markers like rDNA and mtDNA to discover archea i.e. prokaryotes and then for drawing evolutionary tree. But DNA barcoding uses short DNA sequence instead of whole genome and used for eukaryotes. Species can be identified using a short section of DNA from standard region of genome to generate DNA barcode. DNA barcode is short DNA sequence made of four nucleotide bases A (Adenine), T (Thymine), C (Cytosine) and G (Guanine). Each base is represented by a unique color in DNA barcode as shown in fig 1. Even non experts can identify species from small, damaged or industrially processed material. 
Fig.1. DNA Barcode 
DNA barcode should be generated from individual section of DNA. This standard or individual section also known as marker varies among the species. In animals Paul Hebert proposed the use of COI or cox1 present in mitochondrial gene as marker for generating barcode and now it is recognized by International Barcode of Life (IBOL) as official marker for animals. The main reason for choosing mitochondrial gene is because of its small intra specific and large inter specific differences. But COI is not suitable for other group of organisms because it is uniform in them. So ITS (Internal Transcribed Spacer) is recognized for fungus and two genes from chloroplast genome, rbcl and matK are recognized as barcode markers for plants by IBOL. 
The sequence data generated by sequencer are used for identification and to construct a phylogenetic tree. In which related individuals are clustered together. Phylogenetic tree or evolutionary tree is branching diagram which represent the evolutionary history of species. It can provide large amount of information. For a particular species, tree can identify ancestors and closest relatives of species. Suppose if history of animals to be traced through this tree then with the help of this tree many questions can be answered like what earliest animals look liked, what features are inherited by their descendants. 
Fig.2. Evolutionary Tree
A. Applications of DNA Barcoding
1) Controlling agricultural pests
Pest damage in agriculture can cost farmers billion dollars. DNA barcoding can help with this problem by identifying pests in any stage of life which makes it easier to control them. The global Tephritid barcoding initiative contributes to management of fruit flies by providing tools to identify and stop fruit flies at border.
2) Identifying disease vectors
Vector species causes many serious animal and human infectious diseases like malaria. DNA barcoding allows non ecologists to identify these vector species to understand these diseases and cure them. A global mosquito barcoding initiative in building a reference barcode library that can help public health officials to control these diseases causing vector species more effectively and with very less use of insecticides.
3) Sustaining natural resources
Over harvesting of natural resources like hardwood trees and fishes is causing species, extinction and economies collapse of industries that rely on them. Using DNA barcoding natural resource managers can monitor illegal trade of products made of these natural resources. The Fishbol reference barcode is library for hardwood trees, to improve the management and conservation of natural resources.
4) Protecting endangered species
Primate Population is reduced by 90 % in Africa because of bush meat hunting. DNA barcoding can be used by law enforcement to bush meat in local markets which is obtained from bush meat.
5) Monitoring water quality
Drinking water is a process resource for living being. By studying organism living in lakes, rivers and streams, their health can be measured or determined. DNA barcoding is used to create a library of these species that can be difficult to identify. Barcoding can be used by environmental agencies to improve determination of quality and to create better policies which can ensure safe supply of drinking water
6) Routine authentication of natural health products
Authenticity of natural health products is an important, economic, health and conservation issue. Natural health products are often considered as safe because of their natural origin.
7) Identification of plant leaves even if flowers or fruit are not available.
8) Identification of medicinal plants 
B. Procedure of DNA Barcoding
In DNA barcoding there are mainly two steps:
a) Building the barcode library of identified species.
b) Matching the barcode sequence of the unknown sample with the barcode library for its identification.
The first step requires ecologic expertise in selecting one or several individuals per species as reference samples in the barcode library. Tissue samples for generation barcodes are either housed in museum or they can be live specimen in the field. These specimens go through lab processes that are tissue sampling and DNA processing and sequencing to generate DNA barcode in form of chromatogram. Chromatogram is visual representation of DNA sequence produced by sequencer. This barcode produced can be stored in database for future use or can be used as query sequence to be compared with sequence already present in database. 
Fig.3. DNA Barcoding Procedure
Fig.4. Chromatogram of DNA barcode generated by sequencer