Deep Sea is the largest ecosystem in the planet earth serves as a vast reservoir of biodiversity. However, it remains unexplored as only 0.0001% of biodiversity documented from this extreme environment. India is endowed with 2.02 million s.km. area of exclusive economic zone in marine area, of which 60 percent falling under deep sea i.e. above 200 m deep. Zoological Survey of India made a pioneer studies in Indian seas through the oceanographic expeditions of RIMS investigator since from 1874 to 1926. The book provides the consolidated information of deep sea fauna dealing 4371 faunal species based on the data collected over the period of more than 100 years. Contents: 1. Deep-sea biodiversity of India-an overview/Kailash Chandra, C. Raghunathan, Honey U K Pillai, Jasmine P and Tamal Mondal. 2. Protozoa: Ciliata (Planktonic)/Smruthu Mohan, Daizy Bharti, Subhadeep Ghosh, Jasmine P and Santosh Kumar. 3. Foraminifera (Planktonic)/Barbilina Pam and P M. Mohan. 4. Foraminifera (Benthic)/P.M. Mohan and Barbilina Pam. 5. Radiolaria/Aishee Bhowal, Jasmine Purushothaman, C. Raghunathan and Kailash Chandra. 6. Dinoflagellata/Aishee Bhowal, Jasmine Purushothaman, C. Raghunathan and Kailash Chandra. 7. Porifera: Hexactinellida/Preeti Pereria and C. Raghunathan. 8. Cnidaria: Scleractinia/Tamal Mondal and C. Raghunathan. 9. Cnidaria: Octocorallia/J S Yogesh Kumar. 10. Cnidaria: Hydrozoa/Oishinee Chakraborty, Alfisa Siddique, Jasmine Purushothaman, C. Raghunathan and Kailash Chandra. 11. Cnidaria: Scyphozoa/Tamal Mondal and C. Raghunathan. 12. Ctenophora/Alfisa Siddique, Jasmine Purushothaman, C. Raghunathan and Kailash Chandra. 13. Nematoda/Jini Jacob and R. Damodaran. 14. Sipuncula/Tamal Mondal and C. Raghunathan. 15. Echiura/Tamal Mondal and C. Raghunathan. 16. Annelida: Polychaeta/T. Ganesh, Nosad Sahu, Raj Kiran Lakra and S. Balakrishnan. 17. Arthropoda: Pycnogonida/Tamal Mondal and C. Raghunathan. 18. Arthropoda: Crustacea: Copepoda (Planktonic)/Honey U K Pillai and Biju A. 19. Arthropoda: Crustacea: Ostracoda/Alfisa Siddique, Jasmine Purushothaman, C. Raghunathan and Kailash Chandra. 20. Arthropoda: Crustacea: Mysida/Honey U K Pillai and Biju A. 21. Arthropoda: Crustacea: Amphipoda: Hyperiidea/Nair K K C, Honey U K Pillai and Biju A. 22. Arthropoda: Crustacea: Isopoda (Parasitic Cymothoids)/Panakkool Thamban Aneesh, Ameri Kottarathil Helna and Appukuttannair Biju Kumar. 23. Arthropoda: Crustacea: Euphausiacea/Gisha Sivan, Honey U K Pillai and Biju A. 24. Arthropoda: Crustacea: Decapoda: Luciferidae (Planktonic Decapod)/Honey U K Pillai, Biju A and Arya M.S. 25. Arthropoda: Crustacea: Decapoda (Shrimps)/C.P. Rajool Shanis and Bineesh K K. 26. Arthropoda: Crustacea: Decapoda (Lobsters)/C.P. Rajool Shanis and Bineesh K K. 27. Crabs/K. Valarmathi. 28. Brayozoa/Mohammed Naufal, K A Jayaraj and V. Venkatraman. 29. Brachiopoda/Tamal Mondal and C. Raghunathan. 30. Chaetognatha/Alfisa Siddique, Jasmine Purushothaman, C. Raghunathan and Kailash Chandra. 31. Mollusca: Cephalopoda/B Tripathy, AK Mukhopadhyay and S K Sajan. 32. Mollusca: Pteropoda/Alfisa Siddique, Jasmine Purushothaman, C. Raghunathan and Kailash Chandra. 33. Molluscs/S. Rajendra, Tamal Mondal and C. Raghunathan. 34. Echinodermata/C. Surendar, N. Marimuthu and Ch. Satyanarayana. 35. Chordata: Tunicata: Ascidiaceae (Urochordates)/Jhimli Mondal and C. Raghunathan. 36. Pisces/K K Bineesh, S S Mishra and K. Chandra. 37. Pisces (Myctophids)/Meera K.M. and V.N. Sanjeevan. 38. Reptilia: Elapidae: Hydrophiinae/Sonia Mondal and C. Raghunathan. 39. Marine Turtles/Basudev Tripathy. 40. Pelagic Avifauna/V. Gokula and C. Venkataraman. 41. Marine Mammals/Tamal Mondal and C. Raghunathan.