This article addresses the issue of the developer's preliminary contract, including its economic functions. The author attempts to answer the question whether Article 2(2) of the Act on Protecting the Rights of Purchasers of Houses contains an autonomous definition of the "developer's preliminary contract" or it only implies that in some cases the provisions of the above-mentioned Act will be applicable for preliminary contracts concluded on the basis of Article 389 of the Civil Code. Furthermore, the article discusses the issue of the required form for the developer's preliminary contract and the consequences of non-observing it. The author also lists necessary elements of such type of agreement. In conclusions, the author refers to the amendment proposal to the Act on Protecting the Rights of Purchasers of Houses that introduces a new institution, i.e. the defined reservation agreement.