# List of professional services firms in the Loire-Atlantique department

Tamtam tracks 158 professional services firms headquartered in the Loire-Atlantique department. This list ranks the 30 largest by number of employees on LinkedIn, led by Experis France, 𝗚𝗘𝗢𝗙𝗜𝗧 and MCI SAS. Their median headcount is 385. Half of them were founded in 1999 or later. The most common headquarters are Nantes (13), Saint-Herblain (9) and Carquefou (2).

The professional services firms in Loire-Atlantique are primarily mid-sized companies, with headcounts ranging from 385 to over 2,200 employees. Many operate in IT services, consulting, and environmental services. For example, Experis France supports digital transformation projects, while Catamania provides IT consulting and software publishing. Sce Aménagement & Environnement offers urban planning and civil engineering, and DeCA Propreté specializes in cleaning and maintenance services. Bessé is an independent insurance brokerage. The FÉTIS Group provides engineering products and services for various industries, with a focus on decarbonization.

A notable pattern is the concentration of these companies in Nantes and Saint-Herblain, indicating a regional hub for professional services. The founding dates span several decades, from GEOFIT in 1968 to Edeis in 2016, suggesting a mix of established firms and more recently founded companies.

🇫🇷 Loire-Atlantique · 30 companies · Updated Nov 13, 2026

| # | Company | Industry | Headquarters | Employees | Founded |
|---|---|---|---|---|---|
| 1 | [Experis France](https://www.tamtam.ai/c/experis-france) (experisfrance.fr)<br>Supports DSI with innovative digital transformation projects, providing IT services and talent solutions to enhance organizational performance, addressing specific needs. | IT Services and IT Consulting | 🇫🇷 Nantes | 2,207 |  |
| 2 | [𝗚𝗘𝗢𝗙𝗜𝗧](https://www.tamtam.ai/c/company-nantes) (geofit.fr)<br>Designing geographical databases, securing land processes for private and development projects, producing national cartography, developing agriculture, and managing natural resources. | Space Research and Technology | 🇫🇷 Nantes | 1,157 | 1968 |
| 3 | [MCI SAS](https://www.tamtam.ai/c/mci-sas) (mci.fr)<br>This company specializes in commercial and industrial refrigeration, climate engineering, and energy performance optimization for installations across various sectors. | HVAC and Refrigeration Equipment Manufacturing | 🇫🇷 Carquefou | 1,106 | 1963 |
| 4 | [Catamania](https://www.tamtam.ai/c/catamania) (catamania.com)<br>Provides digital transformation services, consulting, software publishing, and information system architecture for banking, insurance, and retail sectors across international agencies using diverse technical expertise. | IT Services and IT Consulting | 🇫🇷 Saint-Herblain | 797 | 1999 |
| 5 | [Sce Aménagement & Environnement](https://www.tamtam.ai/c/sce-amenagement-and-environnement) (sce.fr)<br>Sustainable development firm offering urban planning, civil engineering, and environmental services globally with 45+ years of experience and 500 professionals | Environmental Services | 🇫🇷 Nantes | 625 | 1982 |
| 6 | [Bessé](https://www.tamtam.ai/c/besse) (besse.fr)<br>An independent insurance brokerage company with over 60 years of experience, specializing in protecting businesses and employees with innovative solutions and quality services | Insurance | 🇫🇷 Nantes | 610 | 1960 |
| 7 | [ASI ®](https://www.tamtam.ai/c/asi) (asi.fr)<br>Working towards a responsible digital world dedicated to serving humanity | IT Services and IT Consulting | 🇫🇷 Saint-Herblain | 590 | 1993 |
| 8 | [Conserto](https://www.tamtam.ai/c/conserto) (conserto.pro)<br>Offers IT consulting and expertise services across cloud, digital, and embedded domains through consulting, delivery centers, and labs models. | IT Services and IT Consulting | 🇫🇷 Saint-Herblain | 555 | 2013 |
| 9 | [Abalone France](https://www.tamtam.ai/c/abalone-france) (abalone-interim.com)<br>Specialized in HR services, temporary work, recruitment, and training since 1991, this company focuses on satisfying client needs and increasing employee employability | Human Resources Services | 🇫🇷 Saint-Herblain | 549 | 1991 |
| 10 | [IMATECH](https://www.tamtam.ai/c/imatech) (ima.eu)<br>Development and integration of advanced technology solutions, software services, and digital transformation support for various industries and businesses. | Information Services | 🇫🇷 Nantes | 534 | 1999 |
| 11 | [DeCA Propreté](https://www.tamtam.ai/c/deca-proprete) (deca-proprete.fr)<br>Provides tailored cleaning and maintenance services to professional clients, ensuring high-quality results with advanced techniques and equipment. | Environmental Services | 🇫🇷 Treillières | 501 | 1996 |
| 12 | [FÉTIS Group](https://www.tamtam.ai/c/fetis-group) (fetis.group)<br>Provides engineering products and services for off-road machinery, specialized vehicles, power generation, marine power, and manufacturing industries with focus on decarbonization. | Engineering Services | 🇫🇷 Nantes | 501 | 1978 |
| 13 | [4CAD Group](https://www.tamtam.ai/c/4cad-group) (4cadgroup.com)<br>The company offers PLM, ERP, and IoT tools to help organizations optimize their information systems for increased industrial efficiency | Software Development | 🇫🇷 Bouguenais | 463 | 2004 |
| 14 | [Edeis](https://www.tamtam.ai/c/edeis) (edeis.com)<br>Specializing in engineering, operation, and construction solutions for the future, this company aims to become a leader in construction services and technical management | Engineering Services | 🇫🇷 Nantes | 412 | 2016 |
| 15 | [Atlantic Ingénierie](https://www.tamtam.ai/c/atlantic-ingenierie) (atlantic-ingenierie.com)<br>Engineering firm specializing in energy and telecommunication network deployment, providing expert studies and support for projects of all sizes. | Business Consulting and Services | 🇫🇷 Saint-Herblain | 385 | 2001 |
| 16 | [ALTEREA](https://www.tamtam.ai/c/alterea) (alterea.fr)<br>An all-trade and energy engineering company specializing in renovation, construction, and energy optimization projects across various sectors for over 10 years | Construction | 🇫🇷 Nantes | 318 | 2004 |
| 17 | [AIS](https://www.tamtam.ai/c/ais) (groupeais.fr)<br>AIS is a human-centric company providing expertise to clients since 1985, focusing on professional growth and fulfillment of its employees | IT Services and IT Consulting | 🇫🇷 Saint-Herblain | 289 | 1985 |
| 18 | [SOFRESID ENGINEERING](https://www.tamtam.ai/c/sofresid-engineering) (sofresid-engineering.com)<br>Global engineering company with high value-added services in oil, gas, shipbuilding, steel, and construction industries. Offers turnkey projects, studies, procurement, and supervision. | Engineering Services | 🇫🇷 Saint-Herblain | 230 | 1958 |
| 19 | [Younup](https://www.tamtam.ai/c/younup) (younup.fr)<br>This company offers IT services, supporting clients throughout the software lifecycle from requirements to production, focusing on web, DevOps, data, AI, agility, mobile, and cloud. | IT Services and IT Consulting | 🇫🇷 Nantes | 224 | 2019 |
| 20 | [Slash Intérim](https://www.tamtam.ai/c/slash-interim)<br>Slash Intérim is a national network of temporary recruitment agents, aiming to blend human touch with digital innovation and empower independent recruitment professionals | Human Resources Services | 🇫🇷 Nantes | 203 | 2021 |
| 21 | [COCERTO](https://www.tamtam.ai/c/cocerto) (cocerto.fr)<br>Provides comprehensive accounting, audit, payroll, legal support, and digital tools to optimize and secure business operations with personalized service. | Accounting | 🇫🇷 Nantes | 200 | 1971 |
| 22 | [MECA](https://www.tamtam.ai/c/meca-nantes) (cluster-meca.fr)<br>A cluster of companies offering mechanical analysis expertise to ensure safety and feasibility of constructions through material behavior, design, and stress calculation | Business Consulting and Services | 🇫🇷 Nantes | 194 | 2006 |
| 23 | [GROUPE SYD](https://www.tamtam.ai/c/groupe-syd) (syd.fr)<br>Specializing in digital transformation, the company offers consultancy, project management, infrastructure services, Microsoft solutions integration, application development, and Microsoft expertise, emphasizing customer satisfaction and trust | IT Services and IT Consulting | 🇫🇷 Saint-Herblain | 190 | 1999 |
| 24 | [Compas](https://www.tamtam.ai/c/compas) (lecompas.fr)<br>Specializing in social observation of territories, creating observatories, conducting studies, and providing training for local governments to address social realities effectively | Research Services | 🇫🇷 Nantes | 182 | 1996 |
| 25 | [Cerfrance Loire-Atlantique](https://www.tamtam.ai/c/cerfrance-loire-atlantique) (loire-atlantique.cerfrance.fr)<br>Provide accounting, strategic, fiscal, legal, social, HR, and IT consulting to support local entrepreneurs and business leaders' overall performance. | Business Consulting and Services | 🇫🇷 La Chapelle-sur-Erdre | 177 | 1958 |
| 26 | [SAPRENA](https://www.tamtam.ai/c/saprena) (saprena.com)<br>Creation of sustainable jobs for people with invisible disabilities in sectors like cleaning, landscaping, logistics, industrial maintenance, catering, and packaging. | Business Consulting and Services | 🇫🇷 Bouaye | 169 | 1987 |
| 27 | [ORINOX](https://www.tamtam.ai/c/orinox) (orinox.com)<br>Software consulting and plant design firm specializing in digitalization using AVEVA software suite for engineering, asset data visualization, resources management, simulation, and training | Business Consulting and Services | 🇫🇷 Chateaubriant | 166 | 2008 |
| 28 | [VFLIT - Vous faciliter l'IT](https://www.tamtam.ai/c/vflit-vous-faciliter-l-it) (vousfaciliter-it.fr)<br>Providing integrated cybersecurity, cloud, telecom, management applications, and safety services to enhance organizational IT and communication system performance. | Retail Office Equipment | 🇫🇷 Saint-Sébastien-sur-Loire | 164 | 2000 |
| 29 | [MOCA](https://www.tamtam.ai/c/moca) (asi.fr)<br>MOCA by ASI specializes in offering technical expertise and support for Microsoft solutions to users within the Microsoft ecosystem | IT Services and IT Consulting | 🇫🇷 Saint-Herblain | 159 | 2022 |
| 30 | [Capaciti](https://www.tamtam.ai/c/capaciti) (capaciti.com)<br>A regional leader in cybersecurity, providing specialized services in consulting, engineering, and system infrastructure support with offices in France and international project capabilities | IT Services and IT Consulting | 🇫🇷 Carquefou | 150 | 1999 |

## How this list is built

Every company on this list has a Tamtam company profile. The industry is the one the company gives on LinkedIn; categories such as SaaS or fintech are classified by Tamtam's AI from the company's website and LinkedIn page; and the headquarters city must match the company's own address. Companies are ranked by the number of employees on LinkedIn, and the list is refreshed every night. Classifications can be wrong, so treat the list as a starting point rather than an official ranking. Last updated Nov 13, 2026.

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## The same list elsewhere in France

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- [Professional services firms in Hauts-de-France](https://www.tamtam.ai/l/professional-services-firms-hauts-de-france) (260)
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- [Professional services firms in Paris](https://www.tamtam.ai/l/professional-services-firms-paris) (2,241)
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Source: https://www.tamtam.ai/l/professional-services-firms-loire-atlantique