Exhibit 11.1

ARCADIS GENERAL BUSINESS PRINCIPLES

1.     Introduction

At
ARCADIS we have defined our mission as



In
pursuing this mission as a global company we have identified three core values:Integrity, EntrepreneurshipandAgility.

The
purpose of these General Business Principles is to further develop and implement our commitment toIntegrity.



The
General Business Principles set guidance for our business decisions and actions throughout the world, at all management levels and apply equally to company actions and to individual behaviour of
all our employees in conducting ARCADIS' business.

We
have expressed our principles as a set of commitments and have included in section 3 our approach towards ensuring observance.

2.     Our Commitments

Commitment towards society



Commitment towards clients



1

---





Commitment towards shareholders



Commitment towards employees



Commitment of employees



2

---





Specific commitments



3.     Observance of the General Business Principles



4.     Reporting Violations



3

---





Approved
by the ARCADIS' Supervisory Board
Arnhem, 11 November 2003.

The provisions of the ARCADIS General Business Principles can be amended, supplemented or waived from time to time by resolutions of the ARCADIS Supervisory
Board.

4

---



SUPPLEMENTAL STANDARDS TO THE  ARCADIS General Business Principles  FOR  ARCADIS Senior Financial Officers

ARCADIS
has established certain additional ethical standards for its executive officers and senior financial officers. These officers include the Members of the Executive Board of ARCADIS NV, the
Chief Executive Officer, Chief Financial Officer, Corporate Controller and Controllers of legal entities belonging to the ARCADIS group (the last mentioned group of employees to be designated by the
Chief Financial Officer). These officers must comply with these standards (below) in addition to all of the other standards contained in the ARCADIS General Business Principles.

Integrity and Accuracy of Public Disclosures

ARCADIS's
Members of the Executive Board, the Chief Financial Officer and the above mentioned senior financial officers must take all reasonable steps to ensure that the disclosures in the reports and
documents that ARCADIS files with or submits to the Securities and Exchange Commission and in other public communications are full, fair, accurate, timely and understandable. In the event that the
Members of the Executive Board, the Chief Financial Officer or a senior financial officer learns that any such report, document or communication does not meet this standard and the deviation is
material, then such officer will review and investigate the deviation, advise the Supervisory Board or the ARCADIS Audit Committee and, where necessary, revise the relevant report, document or
communication.

Accounting Treatment

Although
a particular accounting treatment for one or more of ARCADIS's operations may be permitted under applicable accounting standards, the Members of the Executive Board, the Chief Financial
Officer and senior financial officers will not authorize or permit the use of such an accounting treatment if the effect is to distort or conceal ARCADIS's true financial condition.

Amendments and Waivers

Only
the Supervisory Board (or an authorized committee of the Supervisory Board, which shall include the ARCADIS Audit Committee) may waive a part of the General Business Principles, including these
Supplemental Standards, for any senior financial officer, executive officer or director.

ARCADIS
will disclose publicly all material amendments and any waivers for senior financial officers, executive officers or directors, to the extent required by law or by the rules of any securities
exchange to which ARCADIS is subject.

Approved
by the ARCADIS' Supervisory Board
Arnhem, 11 November 2003

5

---



QuickLinks