| Impeto AS | Tromsø | 2005 |
| Implenia Civil Engineering GmbH Nuf | Lysaker | 2008 |
| Implenia Norge AS | Lysaker | 1998 |
| Impregneringsteknikk AS | Billingstad | 2014 |
| Impresa Pizzarotti & C. S.P.A. Nuf | It-43121 Parma | 2019 |
| Ims Va SA | Sandnes | 2021 |
| In Eiendom AS | Brumunddal | 1990 |
| In Mar AS | Bodø | 2022 |
| In Plan AS | Oslo | 2016 |
| In Tre AS | Gjerdrum | 2015 |
| In-Ne AS | Torvastad | 2016 |
| In-Tech Rusztowania Spolka Z Ograniczona Odpowiedzialnoscia Nuf | 78-300 Swidwin | 2025 |
| In-Vesta Bygg AS | Tønsberg | 2016 |
| Inac Process AB Nuf | 444 60 Stora Höga | 2023 |
| Incase Systems AS | Stabekk | 2025 |
| Inch & Si. AS | Svelvik | 2024 |
| Inclu AS | Skodje | 2019 |
| Ind-Tech AS | Sande I Vestfold | 1996 |
| Indal Bygg & Montasje AS | Billingstad | 2022 |
| Indal Invest AS | Billingstad | 2012 |
| Indal Okkenhaug Maskinlag SA | Levanger | 2017 |
| Indergård Bad AS | Snillfjord | 2006 |
| Index Workers D.O.O. Painting Nuf | Si-1241 Kamnik | 2022 |
| Indian Bygg AS | Fetsund | 1998 |
| Indianbosteder AB | Se-68050 Ekshärad | 2007 |
| Indigo AS | Bardu | 2025 |
| Indoor Constructions & Shop Fitting | Pl-84 200 Wejherowo | 2005 |
| Indre Bygg AS | Ørje | 2024 |
| Indre Fosen Entreprenør AS | Leksvik | 2017 |
| Indre Viken Holding AS | Spydeberg | 2016 |
| Indre Østfold Bygg AS | Spydeberg | 2018 |
| Indre Østfold Elektro AS | Mysen | 2003 |
| Indre Østfold Maskin AS | Askim | 2019 |
| Indre Østfold Taktekking AS | Mysen | 2021 |
| Indre Østfold Ventilasjon AS | Askim | 1993 |
| Indre Østfold VVS AS | Askim | 2012 |
| Indrebø Gulvavretting AS | Lillehammer | 2017 |
| Inducon B.V. Nuf | 9411 Se Beilen | 2016 |
| Inductoheat Europe GmbH Nuf | De-73262 Reichenbach An Der Fils | 2026 |
| Indunor AS | Oslo | 2014 |
| Indunor Holding AS | Oslo | 2020 |
| Industisol SAS | Fr-74960 Meythet | 2009 |
| Industri & Bygginstallationer I Norden AB Nuf | Se-45155 Uddevalla | 2025 |
| Industri & Maling AS | Harstad | 2001 |
| Industri Elektro AS | Egersund | 2018 |
| Industri Hjælpern AS | Alta | 2017 |
| Industri Holding AS | Drammen | 2007 |
| Industri Og Rørteknikk AS | Snertingdal | 1999 |
| Industri Og Va Service AS | Hønefoss | 2014 |
| Industri Og VVS Teknikk AS | Oslo | 1996 |
| Industri Plast & Målningsteknik Norden AB | Se-825 31 Iggesund | 2024 |
| Industri Rør AS | Kristiansund N | 2020 |
| Industri- Og Konsulenttjenester AS | Åsgårdstrand | 2006 |
| Industria AS | Bryne | 2014 |
| Industrias Candido Hermida S.L. Nuf | Es-15570 Naron | 2025 |
| Industribelegg AS | Drammen | 2007 |
| Industrielle AS | Tromsø | 2017 |
| Industriemontage Zimmermann E.K. | De-87480 Weitnau | 2025 |
| Industrietechnik Samek GBT | Oslo | 2005 |
| Industrigolv Sweden AB | Se-60234 Norrköping | 2018 |
| Industrigulv Støperen AS | Indre Arna | 2026 |
| Industrigulvspesialisten AS | Godvik | 1997 |
| Industrikulde AS | Tromsdalen | 2018 |
| Industrirør & Gass AS | Sarpsborg | 2020 |
| Industrirør & Gass AS | Sarpsborg | 2025 |
| Industrirørleggern AS | Hov | 2013 |
| Industristillas AS | Sævelandsvik | 2014 |
| Industriteknikk AS | Ånstad | 2017 |
| Industriveien 2 Holmestrand AS | Holmestrand | 2015 |
| Industriveien 37 AS | Heimdal | 2013 |
| Ineco AS | Nyborg | 2026 |
| Ineffable AS | Snarøya | 2020 |
| Inelta Holding AS | Skreia | 2019 |
| Inex Bygg AS | Spongdal | 2016 |
| Infinitta AS | Løten | 2014 |
| Infra Anlegg AS | Fauske | 2006 |
| Infra Group AS | Billingstad | 2021 |
| Infraconstruct Design AS | Tiller | 2021 |
| Infraent AS | Grindvoll | 2025 |
| Infrakon AS | Mo I Rana | 2020 |
| Infrakraft AS | Oslo | 2022 |
| Infrakraft Sverige AB Nuf | Se-653 40 Karlstad | 2022 |
| Infranord AB | Se-171 21 Solna | 2010 |
| Infranord Norge AS | Oslo | 2010 |
| Infratek Norge AS | Oslo | 2002 |
| Infravent AS | Lysaker | 2012 |
| Infura AS | Alta | 2020 |
| Infuture Invest AS | Oslo | 2005 |
| Ing Birger Ådlandsvik AS | Herdla | 2000 |
| Ing Dag Ivar Østby AS | Drammen | 1997 |
| Ing Einar CHR Halvorseth AS | Oslo | 1987 |
| Ing F Wickstrøm AS | Oslo | 1992 |
| Ing Inst F. Isaksen AS | Tromsø | 2006 |
| Ing Morten Fure AS Elektroentreprenøren | Oslo | 1989 |
| Ing Paal Lefdahl Entreprenørforretning AS | Bekkestua | 1990 |
| Ing S D Baastad AS | Oslo | 1985 |
| Ing Thor H Jacobsen AS | Notodden | 1986 |
| Ing Øyvind Jørgensen AS | Stord | 1985 |
| Ing. Robin Svendsen AS | Sortland | 2015 |
| Ing. Trygve Jensen AS | Arendal | 2011 |