[Abstract] This article examines the concept of “professional diligence”, which is the core element of the general clause of the Unfair Commercial Practices Directive (2005/29/EC). It proposes several ways to concrete the concept, in order to avoid as much as possible the uncertainty inherent to the general clause.[Resumen] El artículo examina el concepto de la “diligencia profesional”, núcleo de la cláusula general de la Directiva sobre las prácticas comerciales desleales (2005/29/EC). Se proponen varias maneras para concretar el concepto, de manera que se limite al máximo la incertidumbre inherente a la cláusula genera
