No definition of small and medium undertakings is given in Directive 2009/138 and Delegated Regulation 2015/35.  However, the Commission issued on 6 May 2003 a Recommendation on the definition of micro, small and medium-sized enterprises, aiming at giving guidance to European and national legislators when defining in their national laws such categories of undertakings.

Definitions adapting this recommendation to specific sectors have been adopted in Article 501(2) of Regulation 575/2013, Article 77(1) of Regulation 2017/565 and Article 2(f) of Regulation 2017/1129.