The present research thesis aims to approach installation art in terms of systemic theory; in particular, it focuses on the primary systemic notions of “medium” and “form” and monitors their complex relationship in installation art. After a supervisory introduction to the attempts of defining installation art, its characteristics, and the reasons why installation art continues to fuel an intense discussion in the field of art and its theory, it is supported that installation art is not subjected to only one attempt of definition. Then, the project turns to the descriptive analysis of the parameters of space, time and the spectator, ascertaining that the true expression of installation art is achieved through the cooperation of these parameters. Afterwards, through a primary presentation of the systemic notions of “medium” and “form”, which is accompanied by the theoretical analysis of the distinction between the two terms, the process of coupling their elements and the pivotal role played by the means of the observer’s perception are studied. In other words, the communication produced by installation art and its audience and the process of observing the work of art are described. The analysis continues with the connection of installation art with concepts such as intermediality, corporality and the objects of installation art, but also with the less discussed term of digital ekphrasis, in order to show how the introduction of digital technologies, which entails new possibilities and challenges for art in general, but mainly for installation art, is also added as an extension to the central theoretical part and as a special parameter that establishes installation art as a multimedia - multisensory event. Finally, in each case, the selected theoretical approach is verified and supported through the description and analysis of the appropriately selected works of installation art.