The glossary to understand and take action

Engagement letter

The engagement letter formalises the services agreed between a professional and their client, together with the conditions for their performance.

Notion comptable, fiscale ou juridique · Luxembourg Fiduciaries Editorial Team · Reviewed on

Understand the scope

Definition and points to distinguish

Read the scope, exclusions, information to be provided, fees and arrangements for ending the relationship. An “all-inclusive” formula does not replace a clear description of responsibilities and deliverables.

In your file

What this changes in practice

The engagement letter defines the work entrusted to the professional, the information to be provided and the financial terms. It should make it possible to know who does what: bookkeeping, returns, payroll, advisory services or filing are not automatically included together. Specify the deadlines for providing documents, the validation of deliverables and the arrangements for ending the engagement. Overly general wording encourages omissions and disagreements.

A scenario to help you understand

Educational example

A company entrusts its accounting to a firm and checks whether tax returns, annual filings and data transfer are included in the fees.

Fictitious situation, presented to illustrate the concept.

Prepare for what comes next

Points to check

  • Lister les prestations incluses et exclues
  • Définir les responsabilités de validation
  • Prévoir la fin de mission

The practical question

Find out more

Quelles responsabilités préciser si plusieurs prestataires interviennent ?

Définissez qui reçoit les pièces, contrôle les données, prépare les déclarations, valide et dépose. Précisez également qui répond aux administrations et conserve les preuves. Les interfaces entre paie, comptabilité et conseil fiscal sont particulièrement importantes. Une répartition écrite évite les doubles travaux et les obligations oubliées parce qu’elles n’apparaissent clairement dans aucune mission.

Connecting concepts

Terms to know as well

Continue with the concepts, contacts and procedures related to this topic.

Fiduciary firmA fiduciary firm is a service provider offering, depending on its organisation and authorisations, accounting, tax, administrative or corporate services.Reversibility of accounting dataReversibility refers to the ability to retrieve the documents and data needed to continue management with another tool or service provider.OECThe Ordre des experts-comptables (OEC) is Luxembourg's professional body for the chartered accountancy profession.Chartered accountantThe chartered accountant practises a regulated profession, with assignments relating in particular to accounting and advisory services within the authorised framework.Administrative supportAdministrative support helps prepare and follow up on procedures, documents and deadlines within an agreed scope.SECUlineSECUline is an electronic social-data exchange system used in dealings with the CCSS in accordance with the available procedures.

Put it into practice

Explore further with our guides

Practical guideWhat does a fiduciary firm do? Define the services and engagement letterPractical guideChartered accountant in Luxembourg: roles and status verificationPractical guideChoosing a fiduciary firm in Luxembourg: criteria and questions to askPractical guideAccounting documents: organising filing and retention

Sources and verification

References consulted on 20 September 2026. Official procedures specify the applicable conditions and exceptions.

This guide explains a general process. The applicable rules depend on your situation; it does not constitute personalised advice. Report a correction.

A definition gives you a reference point. To examine your situation, clarify your question with a professional.