There are quite a few directives covering different aspects of procurement.
The main texts are:
- Directive 2014/24/EU on public procurement
- Directive 2014/25/EU on procurement by entities operating in the water, energy, transport and postal services sectors
- Directive 2014/23/EU on the award of concession contracts
You can read the various directives on the EU official website: http://ec.europa.eu/growth/single-market/public-procurement/rules-implementation_en