Tim Robers deals with all private law declarations that, by their very nature, still require supplementation in order for the intended contractual arrangement to be concluded. In doing so, he distinguishes between "blanket" obligations (Blankettschuldverhältnisse) and "blank" declarations in the strict sense (Blanketterklärungen i.e.S.). Blanket obligations are in conflict with the contractual law requirement of certainty. Tim Robers therefore provides a detailed analysis of its content and underlying guiding principles. In addition, the author examines the three central methods by which the parties can specify their obligation: by making the determination themselves (by means of a supplementary agreement), by delegating the power of determination to one party or to a third person, and by an automated linkage to a reference value. It becomes apparent that the constellations governed by §§ 315 et seq. BGB (German Civil Code) are, in dogmatic terms, cases of permitted self-dealing (§ 181 BGB), and that automatic adjustment clauses constitute an autonomous mechanism "in between" self-determination and delegation. Tim Robers explores in depth the consequences of these findings for the interpretation of §§ 315 et seq. BGB and for the legal treatment of automatic adjustment clauses. "Blank" declarations in the strict sense-i.e., texts with gaps that are handed over to another party for completion-are likewise classified as cases of representation. On the dogmatic foundation thus established, the author develops solutions to a wide range of specific issues, for example liability where completion occurs contrary to instructions. For concealed "blank" instruments, he shows that what matters is the distinction between an agent (representative) and a messenger, and he examines this delineation in detail. Finally, the study investigates the potential of the so-called "principles of the blank declaration" for addressing case constellations specific to digitalization.