The paper investigates the role of the principle of proportionality within contract law, in balancing the rights and obligations of the contracting parties. It illustrates that the principle of proportionality is one of the general principles which govern contractual relations, and as such it is an underlying principle of more specific rules of EU contract law. Furthermore, it is investigated whether the principle of proportionality can in addition play a role as an autonomous principle, apart from more specific rules. Finally, some general conclusions about the principle of proportionality in contract law will be formulated.