Digital procurement systems involve a large number of actors with different legal relationships. On the one hand, there are project contracts for setting up and maintaining such systems, including SaaS applications, cloud solutions, data centre operation, outsourcing, etc. On the other hand, the conditions relating to electronic commerce must be regulated between sellers and buyers, with intermediaries or brokers, financial service providers and others. Companies have to evaluate very carefully which European and German regulations apply to B2C and B2B transactions for pure online and mixed online and stationary transactions. Where public purchasers are involved, public procurement provides the obligation to use only electronic communication.