Universal Decimal Classification

  1. Radiation according to wavelength. Hertzian waves. Light colours
  2. Rail transport. Rail traffic
  3. Rail vehicle engineering. Locomotives. Rolling stock. Railway yards. Installations and services concerned with rolling stock
  4. Railways in general. Permanent way. Track construction
  5. Railways. Tramways. Cableways
  6. Rajasthani
  7. Rarefied gases. Vacuum physics
  8. Re-formed churches
  9. Reactions in terms of reagents. Reagents
  10. Records management
  11. Recreation. Entertainment. Games. Sport
  12. Recruitment of forces. Requisition of supplies, resources. War potential. Levies
  13. Recruitment. Missionary activity. Missions broadly. Missiology
  14. Reference works
  15. Regional economics. Territorial economics
  16. Regional economics. Territorial economics. Land economics. Housing economics
  17. Regional geography
  18. Regionalization according to specialized points of view
  19. Regions of ancient American cultures. Pre-Columbian America
  20. Regions of the so-called barbarians
  21. Regressive and reparative processes
  22. Regulation of economic order and control
  23. Regulation of individual sectors of the economy
  24. Regulation of prices, tariffs, finance, credits and accounts
  25. Reinforcement and reparative materials and equipment
  26. Relation between people and state. Internal political activities
  27. Relations between church and state. Policy towards religion. Church policy
  28. Relations between faiths or with society in general. Religion and society
  29. Relations with the public. Regulations for library use
  30. Relative location, direction and orientation
  31. Relief techniques
  32. Religion of the Biblical period. Ancient Judaism. Old Testament religion
  34. Religions characterised by various properties
  35. Religions of antiquity. Minor cults and religions
  36. Religions of China
  37. Religions of classical antiquity
  38. Religions of Europe
  39. Religions of Iran
  40. Religions of Japan
  41. Religions of Korea
  42. Religions of Mesopotamia
  43. Religions of South and Central America. Pre-Columbian indigenous religions
  44. Religions originating in Indian sub-continent. Hindu religion in the broad sense
  45. Religions originating in the Far East
  46. Religious activities. Religious practice
  47. Religious organization and administration
  48. Religious organizations. Religious societies and associations
  49. Religious systems. Religions and faiths
  50. Religious, ecclesiastical architecture. Sacred and funerary buildings
  51. Remote sensing
  52. Renaissance. Baroque. Rococo. Colonial
  53. Reports. Notices. Bulletins
  54. Reproduction. Growth. Development
  55. Reptilia (Reptiles)
  56. Research technique. Preparation. Tabulation
  57. Residents (national or non-national)
  58. Respiration. Breathing. Respiratory system
  59. Réunion (France)
  60. Revived language
  61. Rhaeto-Romance languages
  62. Rhetoric of speech. Art or technique of oral expression
  63. Rhetoric. The effective use of language
  64. Riding
  65. Riding and driving. Horse and other animal sports
  66. Rights and obligations of members
  67. River bank protection. Straightening of rivers and streams. Other river improvement works
  68. Road transport
  69. Rock characteristics and properties generally. Physical and physicochemical petrology
  70. Rodentia. Lagomorpha
  71. Roman Catholic church
  72. Romance / Romanic languages
  73. Romance languages
  74. Romania. Republic of Romania. România
  75. Romanian
  76. Romanian language
  77. Romanian literature
  78. Romanic, 'Latin' peoples
  79. Romany / Gipsy / Gypsy
  80. Rosidae
  81. Rosidae
  82. Runtime environment
  83. Rural engineering
  84. Russia. Russian Federation. Rossiya. Rossiiskaya Federatsiya
  85. Russian
  86. Russian Federation in Asia
  87. Russian language
  88. Russian literature
  89. Rutaceous and moraceous fruits. Citrous fruits in general
  90. Rwanda. Republic of Rwanda