The classic series was written from 1959 to 1979 by 8 different ghostwriters under the pseudonym of Carolyn Keene. The 56 books in the series were meant for children ages 8-12. Because of this, most of the mysteries in this series were theft, arson, hidden wills and inheritances, or the occasional kidnapping. Nancy never solved a murder case and no one ever used inappropriate language.
Nancy's friend, Helen Corning, helped her solve the first four mysteries in the series. After that, cousins Bess Marvin and George Fayne became Nancy's best friends and sleuthing companions. Ned Nickerson was Nancy's boyfriend (although he was usually referred to as her "special" friend), and Bess and George dated Dave Evans and Burt Eddleton. Many of the mysteries came to Nancy through her father, who was a criminal lawyer.
Below is a list of all the books in the series. If you would like to see the illustrations or descriptions, please visit this link. I own all of the books in this series, so if you would like more information, or if you want me to write a review of one of the books, please let me know in the comments section!
1. The Secret of the Old Clock 29. Mystery at the Ski Jump
2. The Hidden Staircase 30. The Clue of the Velvet Mask
3. The Bungalow Mystery 31. The Ringmaster's Secret
4. The Mystery at Lilac Inn 32. The Scarlet Slipper Mystery
5. The Secret of Shadow Ranch 33. The Witch Tree Symbol
6. The Secret of Red Gate Farm 34. The Hidden Window Mystery
7. The Clue in the Diary 35. The Haunted Showboat
8. Nancy's Mysterious Letter 36. The Secret of the Golden Pavilion
9. The Sign of the Twisted Candles 37. The Clue in the Old Stagecoach
10. The Password to Larkspur Lane 38. The Mystery of the Fire Dragon
11. The Clue of the Broken Locket 39. The Clue of the Dancing Puppet
12. The Message in the Hollow Oak 40. The Moonstone Castle Mystery
13. The Mystery of the Ivory Charm 41. The Clue of the Whistling Bagpipes
14. The Whispering Statue 42. The Phantom of Pine Hill
15. The Haunted Bridge 43. The Mystery of the 99 Steps
16. The Clue of the Tapping Heels 44. The Clue in the Crossword Cipher
17. The Mystery of the Brass-Bound Trunk 45. The Spider Sapphire Mystery
18. Mystery of the Moss-Covered Mansion 46. The Invisible Intruder
19. The Quest of the Missing Map 47. The Mysterious Mannequin
20. The Clue in the Jewel Box 48. The Crooked Banister
21. The Secret in the Old Attic 49. The Secret of Mirror Bay
22. The Clue in the Crumbling Wall 50. The Double Jinx Mystery
23. Mystery of the Tolling Bell 51. Mystery of the Glowing Eye
24. The Clue in the Old Album 52. The Secret of the Forgotten City
25. The Ghost of Blackwood Hall 53. The Sky Phantom
26. The Clue of the Leaning Chimney 54. The Strange Message in the Parchment
27. The Secret of the Wooden Lady 55. Mystery of Crocodile Island
28. The Clue of the Black Keys 56. The Thirteenth Pearl
Note: It is believed that the upcoming Nancy Drew computer game, The Silent Spy, is loosely based on the 41st book in this series, The Clue of the Whistling Bagpipes!