| 1 | IS | Island Airlines, Inc. | ICAO: ISA, Callsign: Island, | USA | AVCODES |
| 2 | IS | IDS Aircraft Ltd. d/b/a I.D.S. Heathrow Exective Jets | ICAO: IDS, Callsign: Fanjet, Name changed from IDS Aircraft Ltd. | GB | AVCODES |
| 3 | IS | Intercontinental Pacific Airways, Inc. | ICAO: IPC, Callsign: Interpac, IATA designator changed to IO | RP | AVCODES |
| 4 | IS | IDS Aircraft Ltd. | ICAO: IDS, Callsign: IDS, Name changed to IDS Aircraft Ltd. d/b/a I.D.S. Heathrow Exective Jets | GB | AVCODES |
| 5 | IS | AIS Airlines B.V. | ICAO: PNX, Callsign: Spinner, | NL | AVCODES |
| 6 | IS | Sepehran Airlines | ICAO: SHI, Callsign: Shirazi, | IR | AVCODES |
| 7 | ISA | Island Airlines, Inc. | IATA: IS, Callsign: Island, | USA | AVCODES |
| 8 | ISA | Island Air | Callsign: Island, | USA | AVCODES |
| 9 | ISAA | ISAACS MOVING & STORAGE | | | SCAC4 |
| 10 | ISAE | ISAAC, LEON | | | SCAC4 |
| 11 | ISAF | ISLAND SUPERIOR AIR FILTERS | | | SCAC4 |
| 12 | ISAF | ISAF S.A. | | RO | TRAFFIC |
| 13 | ISAF | ISAF SA | | RO | VKM |
| 14 | ISAH | IONICS MASS SPECTROMETRY GROUP INC | | | SCAC4 |
| 15 | ISAM | ISAM S.r.l. | | IT | VKM |
| 16 | ISAN | INLAND STATE AIR ENTERPRISES INC | | | SCAC4 |
| 17 | ISAP | INTERNATIONAL SEA & AIR SHIPPING | | | SCAC4 |
| 18 | ISAR | ISARIC TRANSPORT INC | | | SCAC4 |
| 19 | ISAR | Isarperle | | D | TRAFFIC |
| 20 | ISAU | NORDIC BULKERS AB | | | SCAC4 |
| 21 | ISAW | INLACO SAIGON | | | SCAC4 |
| 22 | ISAY | INTERNATIONAL SHIPPING AND LOGISTIC | | | SCAC4 |
| 23 | ISB | Caraibes Air Transport | IATA: WS, Callsign: Island Bird, Designator WS recalled by IATA | GP | AVCODES |
| 24 | ISBC | INTEQUIP MINING SALES & SERVICES LT | | | SCAC4 |
| 25 | ISBL | ISABELLA SHIPOWNER S A | | | SCAC4 |
| 26 | ISBU | SEABOARD SYSTEM RAILROAD | | | SCAC4 |
| 27 | ISC | Island Air Charters, Inc. | Callsign: Barracuda, | USA | AVCODES |
| 28 | ISC | Interporto Servizio Cargo | | I | TRAFFIC |
| 29 | ISC | ISC-INTERPORTO Servizi Cargo S.P.A. | | IT | VKM |
| 30 | ISCB | ISABELLA SHIPPING COMPANY | | | SCAC1 |
| 31 | ISCB | ISABELLA SHIPPING COMPANY LTD BERMU | | | SCAC4 |
| 32 | ISCC | INTERNATIONAL SHIPPING COMPANY INC. | | | SCAC4 |
| 33 | ISCF | INTERNATIONAL STONE CONCEPTS | | | SCAC4 |
| 34 | ISCG | INDUSTRIAL SERVICES CONTRACTORS INC | | | SCAC4 |
| 35 | ISCI | INTERNATIONAL TRANSPORT EXPRESS COR | | | SCAC4 |
| 36 | ISCL | INDIA STEAMSHIP (A DIV OF | | | SCAC4 |
| 37 | ISCO | INTERMODAL SALES CORPORATION | | | SCAC4 |
| 38 | ISCP | INSTRON CORP | | | SCAC4 |
| 39 | ISCQ | INTEGRITY SHIPPING CORP | | | SCAC4 |
| 40 | ISCR | INLAND SEAFOOD CORP | | | SCAC4 |
| 41 | ISCT | INTRINSIC TRANSPORT INC | | | SCAC4 |
| 42 | ISCU | STAR CONTAINER SPAIN S.A. | | E | BIC |
| 43 | ISCU | I.S.C. CHEMICALS LTD. | | | PWRC |
| 44 | ISCU | I.S.C. Chemicals | | | RSRV |
| 45 | ISCX | ISC, Inc. | 1/1994-7/2005 | | NAKINA |
| 46 | ISCX | Interlake, Inc. | added 4/1971; 1/1975; eliminated 7/1976 | | NAKINA |
| 47 | ISCX | Interlake Steel Corp. | added 7/1965 (reporting marks changed from IICX); 7/1965-10/1966; eliminated 10/1967 | | NAKINA |
| 48 | ISCX | International Sugar Co. | eliminated 10/1960 | | NAKINA |
| 49 | ISCX | Imperial Sugar Co. | added 7/1960 | | NAKINA |
| 50 | ISCX | Carnegie-Illinois Steel Corp. | 7/1937-4/1938 | | NAKINA |
| 51 | ISCX | Illinois Steel Co. | 7/1935 | | NAKINA |
| 52 | ISCX | Illinois Steel Co. Tank Line | 8/1920-7/1932 | | NAKINA |
| 53 | ISCX | Illinois Steel Co. (Carnegie-Illinois Steel Corp.) | Apr-38 | | NRHS |
| 54 | ISCX | Imperial Sugar Co. | added 7/60 | | NRHS |
| 55 | ISCX | International Sugar Co. | eliminated 10/60 | | NRHS |
| 56 | ISCX | Interlake Steel Corp. | added 7/65 (reporting marks changed from IICX); 7/65-10/66; eliminated 10/67 | | NRHS |
| 57 | ISCX | Interlake, Inc. | added 4/71; 1/75; eliminated 7/76 | | NRHS |
| 58 | ISCX | ISC, Inc. | 1/94-7/2000 | | NRHS |
| 59 | ISCX | *CARNEGIE-ILLINOIS STEEL CORP. [ILLINOIS STEEL CO. TANK LINE] | | | PWRC |
| 60 | ISCX | *INTERNATIONAL SUGAR CO. [IMPERIAL SUGAR CO.] | | | PWRC |
| 61 | ISCX | *INTERLAKE, INC. [INTERLAKE STEEL CORP.] | | | PWRC |
| 62 | ISCX | +ISC, INC. | | | PWRC |
| 63 | ISCX | Illinois Steel Company (ISC Inc.) | | | RSRV |
| 64 | ISCX | ISC INC | | | SCAC4 |
| 65 | ISD | ISD Avia Ltd. | Callsign: Isdavia, | UA | AVCODES |
| 66 | ISD | Innovative Software Design | | ZA | AVCODES |
| 67 | ISD | ISD Avia | | | ICAO1 |
| 68 | ISDE | IRONSIDE ENTERPRISES INC | | | SCAC4 |
| 69 | ISDO | INSIDEOUT ART | | | SCAC4 |
| 70 | ISDU | ISRO DEPARTMENT OF SPACE GOVT OF INDIA | | IND | BIC |
| 71 | ISE | Ise Electric Railway Co. | Owned by Kintetsu | J | TRAFFIC |
| 72 | ISER | Ise Railway | 3. sector railway in Mie Prefecture | J | TRAFFIC |
| 73 | ISES | ISLAND ENTERPRISES | | | SCAC4 |
| 74 | ISEU | I C E SERVICE GROUP INC | | | SCAC4 |
| 75 | ISF | International Stabilisation Assistance Force | Afghanistan Peace keeping forces | GB | AVCODES |
| 76 | ISF | International Sabilisation Assistance Force | | | ICAO1 |
| 77 | ISFD | ISF TRADING INC | | | SCAC4 |
| 78 | ISFF | INTERSCAN SCHIFFAHRTSGESELLSCHAFT M | | | SCAC4 |
| 79 | ISFN | ICICLE SEAFOODS INC | | | SCAC4 |
| 80 | ISFR | ISAAC FREIGHT LIMITED | | | SCAC4 |
| 81 | ISFX | International Sugar Feed Co. | 8/1920-7/1923 | | NAKINA |
| 82 | ISFX | INTERNATIONAL SUGAR FEED CO. | | | PWRC |
| 83 | ISFZ | SEACASTLE CHASSIS | | | SCAC4 |
| 84 | ISG | Sixcargo S.p.A. | IATA: 6P, Callsign: Italcargo, Name changed to Clubair Sixgo S.p.A. | I | AVCODES |
| 85 | ISG | Clubair Sixgo S.p.A. | IATA: 6P, Callsign: Italcargo, Name changed from Sixcargo S.p.A. | I | AVCODES |
| 86 | ISG | Club Air | IATA: 6P | | ICAO1 |
| 87 | ISG | ISG RAILWAYS | | | PWRC |
| 88 | ISG | ISG Railways | | | RSRV |
| 89 | ISGE | ISG EXPRESS INC | | | SCAC4 |
| 90 | ISGI | INTERSTATE SERVICE GROUP INC | | | SCAC4 |
| 91 | ISGL | INTERMODAL SOLUTIONS GROUP LLC | | | SCAC4 |
| 92 | ISGT | ISG TRANSPORTATION INC | | | SCAC4 |
| 93 | ISGU | INCHCAPE SHIPPING SERVICE | | | SCAC4 |
| 94 | ISGX | International Steel Group d/b/a ISG Burns Harbor, Inc. | 7/2005 (not listed) | | NAKINA |
| 95 | ISGX | INTERNATIONAL STEEL GROUP d/b/a ISG BURNS HARBOR, INC. | | | PWRC |
| 96 | ISGX | INTERNATIONAL STEEL GROUP D/B/A ISG | | | SCAC4 |
| 97 | ISH | Island Winds, Inc. | Callsign: Island Hop, | USA | AVCODES |
| 98 | ISHI | INTER SHIP INC | | | SCAC4 |
| 99 | ISHN | INKEL, STEPHANE INC | | | SCAC4 |
| 100 | ISHU | ISLAND SHIPPING LINE LTD. | | | SCAC4 |
