| 301 | IBT | International Bridge and Terminal | | | RSRV |
| 302 | IBT | INTERNATIONAL BRIDGE AND TERMINAL C | | | SCAC4 |
| 303 | IBT | International Bridge & Terminal Co. | | USA | TRAFFIC |
| 304 | IBTE | I-BT EXPRESS LLC | | | SCAC4 |
| 305 | IBTI | INTERSTATE BULK TRANSPORT INC | | | SCAC4 |
| 306 | IBTK | IBARRA TRUCKING | | | SCAC4 |
| 307 | IBTP | IBT | | | SCAC4 |
| 308 | IBTR | I B TRANSPORT INC | | | SCAC4 |
| 309 | IBTU | DEN HARTOGH GLOBAL BV | | NL | BIC |
| 310 | IBTU | UNITED TRANSPORT TANKCONTAINERS BV | | | SCAC4 |
| 311 | IBU | Air-Serv, Inc d/b/a Indigo | IATA: I9, Callsign: Indigo Blue, Designator I9* recalled by IATA. Name changed from Indigo | USA | AVCODES |
| 312 | IBU | Indigo | IATA: I9 | | ICAO1 |
| 313 | IBU | INDUSTRIAL BUS LINES INC | | | SCAC4 |
| 314 | IBUL | IRON BULL HOLDINGS LTD | | | SCAC4 |
| 315 | IBV | IBEROVÍAS EMPRESA CONSTRUCTORA, S.A. | | ES | VKM |
| 316 | IBVL | IBV LLC | | | SCAC4 |
| 317 | IBX | Ibex Airlines Co., Ltd | IATA: FW, Callsign: Ibex, | J | AVCODES |
| 318 | IBX | Ibex Airlines | IATA: FW | | ICAO1 |
| 319 | IBX | IBEX Airlines | | J | TRAFFIC |
| 320 | IBXU | INNOVATION THRU ENERGY CO.,LTD | | J | BIC |
| 321 | IBXW | INSTABOX (WPG) LTD | | | SCAC4 |
| 322 | IBY | International Business Aircraft, Inc. | Callsign: Central Stage, | USA | AVCODES |
| 323 | IBY | International Business Aircraft | | | ICAO1 |
| 324 | IBYU | (TSBY) TUSCOLA & SAGINAW BAY RAILWAY COMPANY | | | PWRC |
| 325 | IBYU | Tuscola and Saginaw Bay Railway | | | RSRV |
| 326 | IBZ | International Business Air | IATA: U5, Callsign: Interbiz, Designator U5 reinstated by IATA | S | AVCODES |
| 327 | IBZ | IBA International Business Airlines AB | IATA: 6I, Callsign: Interbiz, Ceased operations. | S | AVCODES |
| 328 | IBZ | International Business Air | IATA: 6I | | ICAO1 |
| 329 | IC | Indian Airlines Corporation | ICAO: IAC, Callsign: Indair, IATA Prefix: 058, Name changed to NACIL d/b/a Indian Airlines. | IND | AVCODES |
| 330 | IC | NACIL d/b/a Indian Airlines | ICAO: IAC, Callsign: Indair, IATA Prefix: 058, Meregd into Air India. Name changed from Indian Airlines Corporation. | IND | AVCODES |
| 331 | IC | Illinois Central R.R. Co. | added 4/1988; 1/1994-7/2005 | | NAKINA |
| 332 | IC | Illinois Central Gulf R.R. Co. | eliminated 4/1988 | | NAKINA |
| 333 | IC | Illinois Central Gulf R.R. Co. (Illinois Central) | 1/1975-1/1980 | | NAKINA |
| 334 | IC | Illinois Central R.R. Co. | 4/1938-4/1970 | | NAKINA |
| 335 | IC | Illinois Central R.R. Co. (Illinois Central System) | 7/1930-7/1936 | | NAKINA |
| 336 | IC | Illinois Central R.R. Co. | 8/1920-7/1923 | | NAKINA |
| 337 | IC | Illinois Central R.R. Co. | 4/38-4/70 | | NRHS |
| 338 | IC | Illinois Central Gulf R.R. Co. (Illinois Central) | 1/75-1/80 | | NRHS |
| 339 | IC | Illinois Central Gulf R.R. Co. | eliminated 4/88 | | NRHS |
| 340 | IC | Illinois Central R.R. Co. | added 4/88; 1/94-7/2000 | | NRHS |
| 341 | IC | CANADIAN NATIONAL RWY [ILLINOIS CENTRAL GULF RAILROAD; ILLINOIS CENTRAL RR] | | | PWRC |
| 342 | IC | Illinois Central Railroad (Canadian National Railway) | | | RSRV |
| 343 | IC | ILLINOIS CENTRAL RAILROAD COMPANY | | | SCAC4 |
| 344 | IC | Illionis Central | | USA | TRAFFIC |
| 345 | ICA | Icaro | Callsign: Icarfly, | I | AVCODES |
| 346 | ICA | Intercoastal Airways, Inc. | Callsign: Intercoastal, | USA | AVCODES |
| 347 | ICA | Intercontinental Aero Leasing (Pty) Ltd | Callsign: Intercargo, | SD | AVCODES |
| 348 | ICA | Inversiones Tiryka C.A. | Callsign: Tiryka, | YV | AVCODES |
| 349 | ICA | Icaro | | | ICAO1 |
| 350 | ICAC | INTER-CAL CONTRACT CARRIERS | | | SCAC1 |
| 351 | ICAC | INTRA-CAL CONTRACT CARRIERS | | | SCAC4 |
| 352 | ICAL | INTERNATIONAL CARGO LOGISTICS | | | SCAC4 |
| 353 | ICAM | INSULATION CORPORATION OF | | | SCAC4 |
| 354 | ICAO | ICAT LOGISTICS INC | | | SCAC4 |
| 355 | ICAP | HOLIDAY ON ICE | | | PWRC |
| 356 | ICAQ | INTER CANADA A M EXPRESS INC | | | SCAC4 |
| 357 | ICAR | IMPORTACIONES Y EXPORTACIONES CALIF | | | SCAC4 |
| 358 | ICAT | INTER-CAL TRANSPORT | | | SCAC1 |
| 359 | ICAU | ICON INTERNATIONAL CONTAINER SERVICE (AMERICA) LLC | | USA | BIC |
| 360 | ICAU | Icon International Container Service | | | RSRV |
| 361 | ICAX | Inland Refining Co. | 8/1920-7/1923 | | NAKINA |
| 362 | ICAX | INLAND REFINING CO. | | | PWRC |
| 363 | ICB | Islandsflug HF | IATA: HH, Callsign: Icebird, IATA Prefix: 652, Designator HH recalled by IATA. Merged in Air Atlanta Icelandic. IATA designator changed from HT* | IS | AVCODES |
| 364 | ICB | Islandsflug HF | IATA: HT, Callsign: Icebird, IATA designator changed to HH | IS | AVCODES |
| 365 | ICB | Icebird Airline | | | ICAO1 |
| 366 | ICB | In der City Bus GmbH | City: Frankfurt am Main | D | TRAFFIC |
| 367 | ICBI | INTERNATIONAL COMPUTER BROKERS INC | | | SCAC4 |
| 368 | ICBL | Inter City Lines | | USA | TRAFFIC |
| 369 | ICBT | INTERSTATE FREIGHT SYSTEMS INC | | | SCAC4 |
| 370 | ICBU | INTERNATIONAL CONTAINER POOL PTE LTD | | SGP | BIC |
| 371 | ICBU | INTERNATIONAL CONTAINER POOL PTE LT | | | SCAC4 |
| 372 | ICBUS | IC Bus | | D | TRAFFIC |
| 373 | ICBV | ITIRO CORPORATION BVI | | | SCAC4 |
| 374 | ICC | Instituto Cartografico de Cataluna | Callsign: Carto, | E | AVCODES |
| 375 | ICC | Instituto Cartografico de Cataluna | | | ICAO1 |
| 376 | ICCB | INDUSTRIAL CHEMICALS CORPORATION | | | SCAC4 |
| 377 | ICCP | INTERGLOBAL CARGO CORP | | | SCAC4 |
| 378 | ICCU | ICCU CONTAINERS, INC. | | | PWRC |
| 379 | ICCU | ICCU Containers | | | RSRV |
| 380 | ICCX | International Catalyst Corp. | added 10/2001; 7/2005 | | NAKINA |
| 381 | ICCX | Inspiration Consolidated Copper Co. | added 7/1974; 1/1975; eliminated 10/1978 | | NAKINA |
| 382 | ICCX | Industrial Chemical Co. | 8/1920-7/1923 | | NAKINA |
| 383 | ICCX | Inspiration Consolidated Copper Co. | added 7/74; 1/75; eliminated 10/78 | | NRHS |
| 384 | ICCX | *INDUSTRIAL CHEMICAL CO. | | | PWRC |
| 385 | ICCX | *INSPIRATION CONSOLIDATED COPPER CO. | | | PWRC |
| 386 | ICCX | +INTERNATIONAL CATALYST CORP. | | | PWRC |
| 387 | ICCX | International Catalyst Corporation | | | RSRV |
| 388 | ICCX | INTERNATIONAL CATALYST CORPORATION | | | SCAC4 |
| 389 | ICCZ | INTERNATIONAL MINERAL CORP. | | | PWRC |
| 390 | ICD | Icaro S.A. | IATA: X8, Callsign: Icaro, IATA Prefix: 545, Founded in 1971. Ceased operations during 2011. | EC | AVCODES |
| 391 | ICD | Icaro | | | ICAO1 |
| 392 | ICDB | INDIAN CAPITAL DISTRIBUTION CO INC | | | SCAC4 |
| 393 | ICDF | INTERNATIONAL CRUISE DUTY FREE INC | | | SCAC4 |
| 394 | ICDL | INTER-CITY DELIVERY SERVICE, INC | | | SCAC1 |
| 395 | ICDL | INTER-CITY DELIVERY SERVICE INC | | | SCAC4 |
| 396 | ICDP | INTRA CITY DISPATCH INC | | | SCAC4 |
| 397 | ICDU | ICON INT. CONTAINER SERVICE GMBH | | D | BIC |
| 398 | ICDU | ICON INTERNATIONAL CONTAINER SERVIC | | | SCAC4 |
| 399 | ICDUE | I.C.E.F.E DUE SRL | | IT | VKM |
| 400 | ICDV | INTER CITY DELIVERY, INC | | | SCAC1 |
