Short answer
EU law uses two related but distinct procedures. A concrete project may require an environmental impact assessment (EIA) before development consent under Directive 2011/92/EU. A public plan or programme that structures later decision-making may require a strategic environmental assessment (SEA) while it is being prepared under Directive 2001/42/EC.
For EIA, Annex I projects are assessed automatically. Annex II projects must be screened using the Directive's significance criteria. SEA generally covers specified sectoral plans and programmes that frame later EIA-project consents, and plans requiring Habitats assessment. Small local areas, minor modifications and other framework-setting plans require significance screening.
Both procedures must occur while they can still influence the decision, with effective public participation while options remain open. A report produced after approval or construction is not normally a cure. Authorities and courts must eliminate the unlawful consequences. Later regularisation is possible only exceptionally, without circumvention, and must assess past and future effects.
First classify the measure: project or planning framework
An EIA examines construction works, installations, schemes or other interventions. SEA operates one level earlier, examining certain plans and programmes prepared or adopted by an authority and required by legislative, regulatory or administrative provisions.
National labels are not decisive. A circular, order, strategy or zoning amendment can qualify if it establishes criteria and rules for later consents. The same development chain may need SEA for the framework and EIA for the project; one does not replace the other.
In A and Others, C-24/19, the Court held that an order and circular regulating wind-turbine installation and operation required SEA. Splitting rules across instruments cannot evade assessment.
When does a project require EIA?
The controlling rule is prior assessment:
“Member States shall adopt all measures necessary to ensure that, before development consent is given, projects likely to have significant effects on the environment by virtue, inter alia, of their nature, size or location are made subject to a requirement for development consent and an assessment with regard to their effects on the environment.” —
Article 4 then supplies the route:
- Annex I: EIA is mandatory, subject only to the Directive's narrowly framed exemptions.
- Annex II: the Member State decides whether EIA is required by case-by-case examination, thresholds or criteria, or both.
- Screening criteria: the decision must account for Annex III, including the project's characteristics and location and the type and characteristics of its potential effects.
Thresholds cannot exclude Annex II projects that may have significant effects. Screening must consider cumulative effects and sensitive locations.
Under the Directive as amended by Directive 2014/52/EU, the screening determination must be public and state the main reasons by reference to Annex III. A “no EIA” conclusion should identify developer-proposed features relied on to avoid significant effects.
The older Mellor, C-75/08 judgment explains the point: interested parties must be able to decide whether to challenge screening. The current Directive now expressly requires the main reasons.
Two 2025 judgments sharpen the screening safeguards. In C-41/24, the Court held that objective third-party evidence of potentially significant effects can require the authority to obtain and consider additional information from the developer; it may dispense with that step only where objective evidence rules out likely significant effects. In C-236/24, it held that the Directive's conflict-of-interest safeguard applies at screening too: where the screening authority is also the developer, conflicting functions must be appropriately separated.
When does a plan or programme require SEA?
SEA applies to plans and programmes likely to have significant environmental effects. Subject to the small-area and minor-modification rule, Article 3(2) requires assessment for plans and programmes that:
- are prepared for agriculture, forestry, fisheries, energy, industry, transport, waste, water, telecommunications, tourism, town and country planning or land use and set the framework for future consent of projects in the EIA annexes; or
- have been determined to require an appropriate assessment because of likely effects on protected sites under the Habitats Directive.
Small local areas and minor modifications are not automatically exempt: they require SEA where screening finds likely significant effects. Other plans setting a framework for future project consent must also be screened using Annex II criteria, after consulting environmental authorities, with the conclusion made public.
Timing is integral to the obligation:
“The environmental assessment referred to in Article 3 shall be carried out during the preparation of a plan or programme and before its adoption or submission to the legislative procedure.” —
The report must evaluate likely significant effects and reasonable alternatives. Authorities and the public must receive it early enough to comment before adoption. The decision-maker must consider those materials and explain the choice and monitoring.
Participation is part of assessment, not an afterthought
The EU is a party to the Aarhus Convention. Article 6 requires reasonable timeframes and early participation while options are open; Article 7 applies core requirements to environmental plans and programmes. The EIA and SEA Directives implement those principles.
For EIA, the public concerned must receive early information, relevant materials and an effective opportunity to comment. Article 11 requires review of the substantive or procedural legality of covered decisions, acts and omissions. In Stichting Varkens in Nood, C-826/18, the Court held that qualifying environmental organisations cannot be denied review merely because they did not participate earlier.
For SEA, the relevant public—including affected people and environmental organisations—must be identified and given the draft plan and environmental report within appropriate timeframes. Consultation after the political or legal choice has effectively become irreversible does not perform the Directive's preventive function.
Can a missing or defective assessment be cured later?
The starting point is correction, not validation of the accomplished fact. In Wells, C-201/02, the Court held that authorities must take all necessary measures to remedy a missing EIA; depending on national law, this can include revoking or suspending consent so an assessment can be conducted. National procedural rules remain applicable only if they respect equivalence and effectiveness. Compensation may also be relevant where the failure caused harm.
Multi-stage consent does not move the assessment safely to the end. Barker, C-290/03 confirms that if significant effects become apparent at a later consent stage, an EIA must still occur at that stage before the final authorisation is given.
Regularisation is a narrow exception. The Court summarised its conditions in Comune di Corridonia and Others, joined Cases C-196/16 and C-197/16:
“national rules allowing for that regularisation do not provide the parties concerned with an opportunity to circumvent the rules of EU law or to dispense with applying them” and the assessment must also cover environmental impact “from the time of its completion”. —
Regularisation must be authorised by national law, remain exceptional, preserve participation and assess the real baseline, including effects already produced. Commission v Ireland, C-215/06 rejected a retention-permission system that bypassed prior EIA rules without exceptional circumstances.
SEA defects follow a similarly strict remedial logic. National authorities and courts must eliminate the unlawful consequences, normally through suspension or annulment of the defective plan or programme and, where necessary, a consent based upon it. A and Others allowed effects to be maintained only under exceptional conditions, such as a genuine and serious electricity-supply threat that cannot be addressed by alternatives, and only for the period strictly necessary to remedy the illegality. General appeals to renewable-energy policy or administrative convenience are insufficient.
In C-771/24, decided on 9 July 2026, the Court confirmed both the breadth of SEA and the narrow remedy. Regulatory operating rules can be a plan or programme where they establish a significant body of criteria and detailed rules for projects likely to have significant environmental effects. A court may temporarily maintain an SEA-defective regulatory act only where national law permits, this is necessary to ensure transposition of another EU environmental measure, and only for the strictly necessary period.
A practical assessment and remedy checklist
- Identify every decision level and test substance, not national labels.
- For projects, map the activity to Annex I or II and document Annex III screening criteria.
- For plans and programmes, test the sector, framework-setting effect, protected-site link, local-area status and Annex II SEA criteria.
- Begin assessment while alternatives can influence design or adoption; publish reasoned screening conclusions and retain the supporting evidence.
- Give authorities and the public the documents, time and real opportunity to participate.
- If a defect emerges, pause before irreversible steps and identify available suspension, revocation or annulment powers.
- Treat regularisation as exceptional; test circumvention, past effects, public participation and the effect on any downstream consent.
- Check national transposition, limitation periods, standing, interim-relief rules and any parallel Habitats, Water Framework or industrial-emissions assessment.
Conclusion
EIA and SEA are preventive. The question is whether the correct assessment occurred at the correct decision level, before consent or adoption, with reasoned screening and effective participation. Later correction is no substitute for timely assessment: it must remain exceptional, prevent circumvention, examine past and future effects and preserve EU law's practical effectiveness.
Sources
This article provides general legal information, not advice for a specific matter. Laws, facts and procedural deadlines may change the result. Follow the linked primary sources and obtain local advice before acting.