Do we always have to ask for consent before processing personal data?

No. Consent is only one of the six legal bases in paragraph 1. If the processing is necessary for a contract with the data subject (b), for a legal obligation (c) or for a legitimate interest (f), consent is not needed. Recital 43 even points out that consent is not a valid basis where there is a clear imbalance between you and the data subject.

We collected data for purpose A and now want to use it for purpose B. How do we go about that?

Without fresh consent or a legal provision, paragraph 4 requires you to assess whether purpose B is compatible with purpose A. You look at the link between the two purposes, the context in which you collected the data, the nature of the data, the possible consequences for the data subjects and the safeguards in place. Recital 50 adds that with a compatible purpose you need no separate legal basis, but you must still inform the data subject.

Article 6: Lawfulness of processingAI-relevant

Q: When can we rely on legitimate interests?

Paragraph 1(f) requires that the processing is necessary for a legitimate interest of you or a third party, and that the interests and fundamental rights of the data subject do not override it. Recital 47 names the reasonable expectations of the data subject as an important benchmark and gives fraud prevention and direct marketing as examples of possible legitimate interests. Public authorities cannot use this basis for the performance of their tasks.

Praxikon tracks Article 6 (Lawfulness of processing) under the GDPR, alongside the EU AI Act, citing the source for every statement.

Chapter IIIn force since 25-05-2018

Article 6 determines when the processing of personal data is lawful. Paragraph 1 lists six legal bases, at least one of which must apply: consent (a), performance of a contract (b), a legal obligation (c), vital interests (d), a task in the public interest or official authority (e) and legitimate interests (f). Public authorities may not rely on legitimate interests in the performance of their tasks (paragraph 1, last subparagraph). Paragraphs 2 and 3 require that bases (c) and (e) are laid down in Union or Member State law and allow Member States to specify them further. Paragraph 4 gives the factors for assessing whether data may be used for a purpose other than the one for which they were collected.

Key term: Legal basis: one of the six conditions in paragraph 1 that makes processing lawful; without a legal basis, processing is not permitted

Directly affects:controllerprocessordata subjectmember state

Praxikon’s reading of the text and the recitals; the official text below prevails.

AI Act intersection

A valid legal basis is required for processing personal data in AI training data. AI Act Art. 10 indirectly references this GDPR requirement.

AI Act Art. 10 →

Official text

Processing shall be lawful only if and to the extent that at least one of the following applies: (a) the data subject has given consent to the processing of his or her personal data for one or more specific purposes; (b) processing is necessary for the performance of a contract to which the data subject is party or in order to take steps at the request of the data subject prior to entering into a contract; (c) processing is necessary for compliance with a legal obligation to which the controller is subject; (d) processing is necessary in order to protect the vital interests of the data subject or of another natural person; (e) processing is necessary for the performance of a task carried out in the public interest or in the exercise of official authority vested in the controller; (f) processing is necessary for the purposes of the legitimate interests pursued by the controller or by a third party, except where such interests are overridden by the interests or fundamental rights and freedoms of the data subject which require protection of personal data, in particular where the data subject is a child. Point (f) of the first subparagraph shall not apply to processing carried out by public authorities in the performance of their tasks.

Member States may maintain or introduce more specific provisions to adapt the application of the rules of this Regulation with regard to processing for compliance with points (c) and (e) of paragraph 1 by determining more precisely specific requirements for the processing and other measures to ensure lawful and fair processing including for other specific processing situations as provided for in Chapter IX.

The basis for the processing referred to in point (c) and (e) of paragraph 1 shall be laid down by: (a) Union law; or (b) Member State law to which the controller is subject. The purpose of the processing shall be determined in that legal basis or, as regards the processing referred to in point (e) of paragraph 1, shall be necessary for the performance of a task carried out in the public interest or in the exercise of official authority vested in the controller. That legal basis may contain specific provisions to adapt the application of rules of this Regulation, inter alia: the general conditions governing the lawfulness of processing by the controller; the types of data which are subject to the processing; the data subjects concerned; the entities to, and the purposes for which, the personal data may be disclosed; the purpose limitation; storage periods; and processing operations and processing procedures, including measures to ensure lawful and fair processing such as those for other specific processing situations as provided for in Chapter IX. The Union or the Member State law shall meet an objective of public interest and be proportionate to the legitimate aim pursued.

Where the processing for a purpose other than that for which the personal data have been collected is not based on the data subject's consent or on a Union or Member State law which constitutes a necessary and proportionate measure in a democratic society to safeguard the objectives referred to in Article 23(1), the controller shall, in order to ascertain whether processing for another purpose is compatible with the purpose for which the personal data are initially collected, take into account, inter alia: (a) any link between the purposes for which the personal data have been collected and the purposes of the intended further processing; (b) the context in which the personal data have been collected, in particular regarding the relationship between data subjects and the controller; (c) the nature of the personal data, in particular whether special categories of personal data are processed, pursuant to Article 9, or whether personal data related to criminal convictions and offences are processed, pursuant to Article 10; (d) the possible consequences of the intended further processing for data subjects; (e) the existence of appropriate safeguards, which may include encryption or pseudonymisation.

Source: EUR-Lex, Regulation (EU) 2016/679. Official text, reproduced without modification.

What does this mean for you?

Controller

Before each processing operation, decide which legal basis in paragraph 1 you rely on and record it. If you choose legitimate interests (paragraph 1(f)), you must weigh your interest against the interests and fundamental rights of the data subject, with extra weight where a child is involved; recital 47 names the reasonable expectations of the data subject as the yardstick. If you want to use data for a new purpose, for example to train an AI model, you run the compatibility test of paragraph 4, unless you have fresh consent or a legal provision that allows it.

Processor

The legal basis belongs to the controller; as a processor you cannot choose a legal basis yourself. If you use the data for a purpose of your own, you are no longer a processor for that part and need your own legal basis under paragraph 1.

Data Protection Officer

Check that a legal basis is recorded for every processing operation and that it fits the situation: recital 43 warns that consent is not a valid basis where there is a clear imbalance, for example between a public authority and a citizen. Guard the compatibility test of paragraph 4 whenever someone proposes using data for a different purpose.

Data Subject

An organisation may process your data only if one of the six legal bases in paragraph 1 applies. If it relies on legitimate interests, your interests and fundamental rights must not override that interest (paragraph 1(f)). When data are used for another purpose, recital 50 says the organisation must inform you about that purpose and about your rights, including the right to object.

Compliance checklist

For every processing operation the legal basis under Article 6(1) is recorded before processing starts.Where consent is the legal basis, it was given for one or more specific purposes (Article 6(1)(a)).Where legitimate interests are relied on, a documented balancing exists between the organisation's interest and the interests and fundamental rights of the data subject, with particular attention to children (Article 6(1)(f)).Public authorities do not use legitimate interests as a legal basis for the performance of their tasks (Article 6(1), last subparagraph).Where a legal obligation or public task is relied on, the Union or national provision that forms the basis is identified (Article 6(3)).Where data are processed for a purpose other than the original one, the compatibility test has been carried out using the factors in Article 6(4).For further processing it has been assessed whether appropriate safeguards, such as encryption or pseudonymisation, are in place (Article 6(4)(e)).

Related recitals

(40)

In order for processing to be lawful, personal data should be processed on the basis of the consent of the data subject concerned or some other legitimate basis, laid down by law, either in this Regul...

(41)

Where this Regulation refers to a legal basis or a legislative measure, this does not necessarily require a legislative act adopted by a parliament, without prejudice to requirements pursuant to the c...

(42)

Where processing is based on the data subject's consent, the controller should be able to demonstrate that the data subject has given consent to the processing operation. In particular in the context ...

(43)

In order to ensure that consent is freely given, consent should not provide a valid legal ground for the processing of personal data in a specific case where there is a clear imbalance between the dat...

(44)

Processing should be lawful where it is necessary in the context of a contract or the intention to enter into a contract....

(45)

Where processing is carried out in accordance with a legal obligation to which the controller is subject or where processing is necessary for the performance of a task carried out in the public intere...

(46)

The processing of personal data should also be regarded to be lawful where it is necessary to protect an interest which is essential for the life of the data subject or that of another natural person....

(47)

The legitimate interests of a controller, including those of a controller to which the personal data may be disclosed, or of a third party, may provide a legal basis for processing, provided that the ...

(48)

Controllers that are part of a group of undertakings or institutions affiliated to a central body may have a legitimate interest in transmitting personal data within the group of undertakings for inte...

(49)

The processing of personal data to the extent strictly necessary and proportionate for the purposes of ensuring network and information security, i.e. the ability of a network or an information system...

(50)

The processing of personal data for purposes other than those for which the personal data were initially collected should be allowed only where the processing is compatible with the purposes for which...

Cross-references

Art. 9: Processing of special categories of personal data Art. 10: Processing of personal data relating to criminal convictions and offences Art. 23: Restrictions

Frequently asked questions

← Art. 5: Principles relating to processing of personal data Art. 7: Conditions for consent →

Connections

Themes where this returns

Data quality, minimisation and data governance

The counterpart in the other law

Article 10 AI Act: Data and data governance
via Data quality, minimisation and data governance

Case law

EU Court of Justice in KNLTB: a purely commercial interest can be a legitimate interest
2024-10-04 · final, Hof van Justitie van de Europese Unie
Noord-Nederland District Court upholds DPA fine for village livestream, reduces it to 375 euros
2025-01-09 · status not established, Rechtbank Noord-Nederland
Council of State: 600,000 euro fine for wifi tracking in Enschede stays annulled
2026-07-29 · final, Raad van State, Afdeling bestuursrechtspraak
Mousse: asking for Mr or Ms when selling a train ticket is not necessary
2025-01-09 · final, Hof van Justitie van de EU (Eerste kamer), Mousse tegen Commission nationale de l'informatique et des libertés (CNIL) en SNCF Connect
Overijssel District Court revokes DPA fine for wifi tracking in Enschede
2024-02-02 · final, Rechtbank Overijssel
Interim relief judge: DPA must redact fine amount when giving an enforcement decision to complainants
2024-05-31 · status not established, Rechtbank Den Haag, voorzieningenrechter (kort geding, team handel)
Meta v Bundeskartellamt: competition authority may find a GDPR breach, strict conditions for legal bases behind personalised advertising
2023-07-04 · final, Hof van Justitie van de EU (Grote kamer), Meta Platforms Inc., Meta Platforms Ireland Ltd en Facebook Deutschland GmbH tegen Bundeskartellamt