# Top 30 consulting firms in the Hauts-de-Seine department

Tamtam tracks 563 consulting firms headquartered in the Hauts-de-Seine department. This list ranks the 30 largest by number of employees on LinkedIn, led by ALTEN, Altran and Devoteam. Their median headcount is 3,243. Half of them were founded in 1989 or later. The most common headquarters are Boulogne-Billancourt (8), Neuilly-sur-Seine (6) and Levallois-Perret (4).

These companies in Hauts-de-Seine are primarily large consulting firms, specializing in IT, engineering, and business services. Notable examples include ALTEN, which provides engineering and IT services, and Devoteam, an AI-driven tech consulting firm. Forvis Mazars Group offers audit, tax, and advisory services, while Apave specializes in technical and environmental risk management. Assystem focuses on nuclear engineering and energy transition, and TRIGO provides quality solutions for automotive, aerospace, and transport industries.

The headquarters of these major firms are concentrated in a few key cities within Hauts-de-Seine. Boulogne-Billancourt, Neuilly-sur-Seine, and Levallois-Perret emerge as central hubs, hosting a significant number of these large employers. A common founding era is also observed, with many of these companies, such as ALTEN and Astek, established around the late 1980s.

🇫🇷 Hauts-de-Seine · 30 companies · Updated Nov 12, 2026

| # | Company | Industry | Headquarters | Employees | Founded |
|---|---|---|---|---|---|
| 1 | [ALTEN](https://www.tamtam.ai/c/alten) (alten.com)<br>Provides engineering and IT services, supporting businesses in technological and sustainable transformation across various industries with high-level consultant-engineers. | Engineering Services | 🇫🇷 Boulogne-Billancourt | 38,710 | 1988 |
| 2 | [Altran](https://www.tamtam.ai/c/altran) (capgemini-engineering.com)<br>Altran, now Capgemini Engineering, offers engineering services Follow them on LinkedIn for updates and insights | IT Services and IT Consulting | 🇫🇷 Neuilly-sur-Seine | 11,652 |  |
| 3 | [Devoteam](https://www.tamtam.ai/c/devoteam) (devoteam.com)<br>AI-driven tech consulting firm specializing in cloud platforms, cyber, data, and sustainability, guiding businesses through sustainable digital transformation to deliver value. | Business Consulting and Services | 🇫🇷 Levallois-Perret | 10,274 |  |
| 4 | [Apave](https://www.tamtam.ai/c/apave) (apave.com)<br>Specializes in technical, human, environmental, and digital risk management, ensuring safety and performance across various economic sectors for over 150 years. | Environmental Services | 🇫🇷 Courbevoie | 9,778 | 1867 |
| 5 | [Forvis Mazars Group](https://www.tamtam.ai/c/forvis-mazars-group) (forvismazars.com)<br>International partnership delivering audit, tax, and advisory services across one hundred countries and territories through an integrated global professional services network. | Accounting | 🇫🇷 Levallois-Perret | 9,534 |  |
| 6 | [Assystem](https://www.tamtam.ai/c/assystem) (assystem.com)<br>Independent nuclear engineering company accelerating energy transition, developing nuclear and renewable energies, power grids, hydrogen projects, and low-carbon transport. | Business Consulting and Services | 🇫🇷 Courbevoie | 8,143 |  |
| 7 | [Astek](https://www.tamtam.ai/c/astek) (astekgroup.fr)<br>Supports clients with high-value service, deep technical expertise across technology, operations, and engineering, focusing on sustainable digital transformation with humans at the core. | IT Services and IT Consulting | 🇫🇷 Boulogne-Billancourt | 6,035 | 1988 |
| 8 | [TRIGO](https://www.tamtam.ai/c/trigo) (trigo-group.com)<br>Provides comprehensive quality solutions and management services for automotive, aerospace, and transport industries, addressing supply chain challenges globally with local expertise. | Business Consulting and Services | 🇫🇷 Nanterre | 5,771 | 1997 |
| 9 | [Vulcain Engineering Group](https://www.tamtam.ai/c/vulcain-engineering-group) (vulcain-eng.com)<br>Provides engineering consulting and project solutions for energy and environmental sectors, delivering technical assistance, expertise, and project management globally. | Business Consulting and Services | 🇫🇷 Neuilly-sur-Seine | 5,234 | 2005 |
| 10 | [Synergie France](https://www.tamtam.ai/c/synergie-france) (synergie.fr)<br>French leader in HR services: recruitment, training, and HR consulting Providing solutions in various sectors, emphasizing proximity, performance, and diversity | Human Resources Services | 🇫🇷 Boulogne-Billancourt | 4,804 |  |
| 11 | [OPEN](https://www.tamtam.ai/c/open-levallois-perret) (open.global)<br>Supports large companies and public organizations in digital transformation, focusing on technological performance, sovereignty, digital sobriety, and scaling innovations with advanced solutions. | IT Services and IT Consulting | 🇫🇷 Levallois-Perret | 4,705 | 1989 |
| 12 | [BNP Paribas Real Estate](https://www.tamtam.ai/c/bnp-paribas-real-estate) (bnpparibas.com)<br>Offers comprehensive real estate services including property development, transactions, consulting, valuation, and property management across Europe, the Middle East, and Asia. | Real Estate | 🇫🇷 Boulogne-Billancourt | 4,173 | 1963 |
| 13 | [PwC France](https://www.tamtam.ai/c/pwc-france) (pwc.fr)<br>Offers consulting, audit, legal, and tax expertise, blending technology with multidisciplinary knowledge to accelerate sustainable business transformation for organizations. | Business Consulting and Services | 🇫🇷 Neuilly-sur-Seine | 4,109 |  |
| 14 | [Scalian](https://www.tamtam.ai/c/scalian) (scalian.com)<br>A global company founded in 1989 with 3 business lines focusing on Digital Transformation, Digital Systems, and Operations Performance across various countries | Business Consulting and Services | 🇫🇷 Neuilly-sur-Seine | 4,098 | 1989 |
| 15 | [Leyton](https://www.tamtam.ai/c/leyton) (leyton.com)<br>International consulting firm helps businesses leverage financial incentives for growth and long-lasting performance by simplifying access to complex benefits. | Business Consulting and Services | 🇫🇷 Issy-les-Moulineaux | 3,243 | 1997 |
| 16 | [VISEO](https://www.tamtam.ai/c/viseo) (viseo.com)<br>Assists clients globally with digital and business transformation using advanced technology and industry expertise for productivity, innovation, and competitiveness. | IT Services and IT Consulting | 🇫🇷 Boulogne-Billancourt | 3,016 | 1999 |
| 17 | [SE Advisory Services](https://www.tamtam.ai/c/se-advisory-services) (seadvisoryservices.com)<br>Helps organizations achieve sustainability, energy, and digitalization goals through expertise, global implementation, and AI-powered software, turning challenges into advantages. | Business Consulting and Services | 🇫🇷 Rueil-Malmaison | 2,948 |  |
| 18 | [Grant-Thornton France](https://www.tamtam.ai/c/grant-thornton-france) (grantthornton.fr)<br>Provides audit, financial advisory, operational consulting, legal and tax advice, and sustainable transformation services to French businesses. | Financial Services | 🇫🇷 Neuilly-sur-Seine | 2,342 | 1964 |
| 19 | [Apside](https://www.tamtam.ai/c/apside) (apside.com)<br>Provides consulting, engineering in Information Systems, Technical and Scientific Computing, Automotive and Financial Engineering, for large French and European groups. | IT Services and IT Consulting | 🇫🇷 Boulogne-Billancourt | 2,300 | 1976 |
| 20 | [Ingérop](https://www.tamtam.ai/c/ingerop) (ingerop.fr)<br>An independent engineering company with expertise in infrastructure, transportation, water, environment, energy, and industrial facilities in over 70 countries | Engineering Services | 🇫🇷 Rueil-Malmaison | 2,268 | 1992 |
| 21 | [agap2](https://www.tamtam.ai/c/agap2) (agap2.com)<br>Global consulting firm specializing in industries and information systems, creating value for customers and consultants through innovation and extensive technical know-how. | Business Consulting and Services | 🇫🇷 Boulogne-Billancourt | 2,075 | 2005 |
| 22 | [Ayming](https://www.tamtam.ai/c/ayming) (ayming.com)<br>Partners with businesses, institutions to unlock lasting value. Translates policy into opportunities, manages growth transformation. Specializes in innovation, HR, taxes across 14 countries. Delivers tangible results beyond consulting. | Business Consulting and Services | 🇫🇷 Levallois-Perret | 1,947 | 1986 |
| 23 | [Infotel](https://www.tamtam.ai/c/infotel) (infotel.com)<br>Provides IT and digital transformation consulting for large enterprises, focusing on strategic design, technological expertise, and agile development, from conception to implementation. | IT Services and IT Consulting | 🇫🇷 Neuilly-sur-Seine | 1,894 | 1979 |
| 24 | [Extia](https://www.tamtam.ai/c/extia) (extia-group.com)<br>Offers IT consulting services across various sectors, focusing on employee well-being to drive project success and client performance with a collaborative approach. | IT Services and IT Consulting | 🇫🇷 Sèvres | 1,881 | 2007 |
| 25 | [Davidson consulting](https://www.tamtam.ai/c/davidson-consulting) (davidson.fr)<br>A management consulting and technology company with over 2,000 employees, expanding internationally with a focus on employee well-being and creativity | Business Consulting and Services | 🇫🇷 Boulogne-Billancourt | 1,843 | 2005 |
| 26 | [Sofrecom](https://www.tamtam.ai/c/sofrecom) (sofrecom.com)<br>Advises, guides, and supports telecommunications players' digital transformation and green transition, offering business, network, and IT consulting for improved operational performance. | IT Services and IT Consulting | 🇫🇷 Châtillon | 1,469 | 1966 |
| 27 | [ProductLife Group](https://www.tamtam.ai/c/productlife-group) (productlifegroup.com)<br>Global service provider in Life Sciences, delivering end-to-end consulting and outsourcing services across the entire product lifecycle for various sectors. | Pharmaceutical Manufacturing | 🇫🇷 Courbevoie | 1,469 |  |
| 28 | [Niji](https://www.tamtam.ai/c/niji) (niji.fr)<br>Provides consulting, design, and technology implementation for digital transformation in businesses and public organizations, including Salesforce integration and cybersecurity. | IT Services and IT Consulting | 🇫🇷 Issy-les-Moulineaux | 1,460 | 2001 |
| 29 | [Cegos France](https://www.tamtam.ai/c/cegos-france) (cegos.fr)<br>Provides extensive professional training and development programs across management, leadership, HR, marketing, and project management internationally with expert consultants. | Professional Training and Coaching | 🇫🇷 Issy-les-Moulineaux | 1,259 | 1926 |
| 30 | [Alkera](https://www.tamtam.ai/c/alkera) (alkera.fr)<br>French independent group, risk and claims management for insurers, brokers, and businesses. Offers pre- and post-claim services, including audit, expertise, repair, and delegation. | Insurance | 🇫🇷 Clichy | 1,213 |  |

## 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 12, 2026.

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## The same list elsewhere in France

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- [Consulting firms in the Rhône department](https://www.tamtam.ai/l/consulting-firms-rhone) (242)
- [Consulting firms in Occitanie](https://www.tamtam.ai/l/consulting-firms-occitanie) (236)
- [Consulting firms in Provence-Alpes-Côte d'Azur](https://www.tamtam.ai/l/consulting-firms-provence-alpes-cote-dazur) (233)
- [Consulting firms in Nouvelle-Aquitaine](https://www.tamtam.ai/l/consulting-firms-nouvelle-aquitaine) (166)
- [Consulting firms in Grand Est](https://www.tamtam.ai/l/consulting-firms-grand-est) (165)
- [Consulting firms in Hauts-de-France](https://www.tamtam.ai/l/consulting-firms-hauts-de-france) (161)
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- [Consulting firms in the Nord department](https://www.tamtam.ai/l/consulting-firms-nord) (115)
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- [Consulting firms in the Loire-Atlantique department](https://www.tamtam.ai/l/consulting-firms-loire-atlantique) (94)
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- [Consulting firms in the Isère department](https://www.tamtam.ai/l/consulting-firms-isere) (57)
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- [Consulting firms in Neuilly-sur-Seine](https://www.tamtam.ai/l/consulting-firms-neuilly-sur-seine) (73)

## The same list elsewhere

- [Consulting firms in the world](https://www.tamtam.ai/l/consulting-firms-in-the-world) (16,009)
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Source: https://www.tamtam.ai/l/consulting-firms-hauts-de-seine