The oldest method of involving the European Parliament in EU legislation.
The EU Commission and Council consulted the European Parliament by sending a document to it before the content was made law (pre-legislative). The Parliament could decide upon an opinion by a simple majority.
The Commission and Council had no duty to follow, or even read, the response of the Parliament. But they had to respect the procedure. In the so-called isoglucose-case the European Parliament got the EU Court to annul a decision which was made without the consultation procedure being properly followed.
The Lisbon Treaty has made co-decision the general rule for EU legislation, giving the European Parliament more influence.
Links
Consultation procedure in Scadplus http://europa.eu/scadplus/glos....../consultation_procedure_en.htm