- Isaac
- Isaac Asimov
- Isaac Bashevis Singer
- Isaac Hull
- Isaac M. Singer
- Isaac Mayer Wise
- Isaac Merrit Singer
- Isaac Newton
- Isaac Stern
- Isaac Watts
- Isabella
- Isabella I
- Isabella Stewart Gardner
- Isabella the Catholic
- Isadora Duncan
- Isaiah
- Isak Dinesen
- Isamu Noguchi
- isarithm
- Isatis
- Isatis tinctoria
- ischaemia
- ischaemic
- ischaemic stroke
- ischemia
- ischemic
- ischemic anoxia
- ischemic hypoxia
- ischemic stroke
- Ischia
- ischial bone
- Ischigualastia
- ischium
- isentropic
- Isere
- Isere River
- Iseult
- Isfahan
- Isherwood
- Ishmael
- Ishtar
- ISI
- Isidor Feinstein Stone
- Isidore Auguste Marie Francois Comte
- isinglass
- Isis
- ISKCON
- Islam
- Islam Nation
- Islamabad
- Islamic
- Islamic Army of Aden
- Islamic Army of Aden-Abyan
- Islamic calendar
- Islamic calendar month
- Islamic Community
- Islamic Great Eastern Raiders-Front
- Islamic Group
- Islamic Group of Uzbekistan
- Islamic Jihad
- Islamic Jihad for the Liberation of Palestine
- Islamic law
- Islamic Party of Turkestan
- Islamic Republic of Iran
- Islamic Republic of Mauritania
- Islamic Republic of Pakistan
- Islamic Resistance Movement
- Islamic State of Afghanistan
- Islamic Ummah
- Islamic Unity
- Islamise
- Islamism
- Islamist
- Islamize
- Islamophobia
- island
- island dispenser
- island hop
- island of Guernsey
- island of Jersey
- island-dweller
- islander
- islands of Langerhans
- islay
- isle
- Isle of Man
- Isle of Skye
- Isle of Wight
- Isle Royal National Park
- isles of Langerhans
- Isles of Scilly
- islet
- islets of Langerhans
- ism
- Ismaili
- Ismailian
- Ismailism
- ISN
- isoagglutination
- isoagglutinin
- isoagglutinogen
- isoantibody
- isobar
- isobilateral
- isobutyl nitrite
- isobutylene
- isobutylphenyl propionic acid
- isocarboxazid
- isochronal
- isochrone
- isochronous
- isoclinal
- isoclinic
- isoclinic line
- Isocrates
- isocyanate
- isocyanic acid
- isocyclic
- Isoetaceae
- Isoetales
- Isoetes
- isoflurane
- isogamete
- isogamy
- isogon
- isogonal line
- isogone
- isogonic
- isogonic line
- isogram
- isohel
- isolable
- isolate
- isolated
- isolating
- isolation
- isolationism
- isolationist
- isolationistic
- Isolde
- Isole Egadi
- isoleucine
- isomer
- isomerase
- isomeric
- isomerisation
- isomerise
- isomerism
- isomerization
- isomerize
- isometric
- isometric exercise
- isometric line
- isometrical
- isometrics
- isometropia
- isometry
- isomorphic
- isomorphism
- isomorphous
- isomorphy
- isoniazid
- isopleth
- isopod
- Isopoda
- isopropanol
- isopropyl alcohol
- isoproterenol
- Isoptera
- isopteran
- Isoptin
- Isopyrum
- Isopyrum biternatum
- Isordil
- Isoroku Yamamoto
- isosceles
- isosceles triangle
- isosmotic
- isosmotic solution
- isosorbide
- Isospondyli
- isostasy
- isotherm
- isothermal
- isothermic
- isothiocyanate
- isotonic
- isotonic exercise
- isotonic solution
- isotope
- isotopic
- isotropic
- isotropically
- isotropous
- isotropy
- Israel
- Israel Baline
- Israel Strassberg
- Israel Zangwill
- Israeli
- Israeli Defense Force
- Israeli monetary unit
- Israelite
- Israelites
- Issachar
- issuance
- issue
- issue forth
- issuer
- issuing
- Issus
- Istanbul
- isthmian
- Isthmian Games
- isthmus
- Isthmus of Corinth
- Isthmus of Darien
- Isthmus of Kra
- Isthmus of Panama
- Isthmus of Suez
- Isthmus of Tehuantepec
- Istiophoridae
- Istiophorus
- Istiophorus albicans
- Isuprel
- Isuridae
- Isurus
- Isurus glaucus
- Isurus oxyrhincus
- Isurus paucus
