Authenticity is one of the most prominent factors determining the value of an art work as well as conservation theory and praxis. It exerts prime impact on defining decision strategies, and the significance, preservation, exposition and conservation-restoration of a given work. It also determines the form in which it will be passed on to future generations. In the past, criteria applied for assessing authenticity underwent a number of changes, and by the twentieth century they assumed a form defined in assorted codes of conservation ethics and procedure. Authenticity, however, is not an absolute and constant value, but succumbs to perennial transformations and reflects new truths and criteria. The article attempts to answer these questions within the domain of select problems and upon the basis of most recent international accomplishments. Philosophical premises act as a point of departure for a discussion on the conditions of the preservation of the authenticity of a contemporary art work, with the authoress considering the authenticity of matter, conception and context as well as differentiated approaches to the protection of old art according to the principles of technological correctness. Other questions involve the specificity, techniques and technology of present-day art and its impact on preservation and permanence. The presented reflections pertain to the uniqueness of the conception of a work of art, which can be detected by studying not only its structure but predominantly the artist's intentions. Just as important is the establishment of the context of space, place, culture or history. Attention is drawn to the necessity of distinguishing the complexity of particular, haptic-optic elements of the work of art and their mutual relations, which leads to the preservation of inner unity. The assorted problems are illustrated with examples of Polish and world art in whose cases the comprehension of authenticity was neither obvious nor unambiguous, and frequently resulted in falsifying the original message. Finally, the article examines the newest world tendencies and paths of conservation and protection, which designate the tasks, methods, forms and purposes of ventures intent on preserving the modern work of art together with 'in the full richness of their authenticity'.