The publication provides an analysis of the legal bases applicable to public procurement contracts against the background of specific problems encountered in the implementation of construction investments. It sets out, among other things, the principles of changes to contracts introduced by the new Act - Public Procurement Law dated 11.09.2019, which will apply to contracts concluded as a result of contract award procedures initiated after 31.12.2020, together with comparison of them with the existing regulation; discussing the individual statutory conditions for amending the contract; classifying clauses for amending the contract together with attributing certain legal effects to them; Polish and European jurisprudence on changes to contracts; specific rules for shaping the description of the object of the contract for works. Addressees: The book is intended for lawyers of practitioners, administrative staff involved in preparing and executing public procurement procedures, as well as for entrepreneurs from the construction industry - contractors of public buildings, roads, railway infrastructure. It will be a valuable source of knowledge for academics and law and administration students.