This introductory chapter explores the genesis of the term ‘transdisciplinarity’ and its conceptual crystallisation, beginning in the 1970s, in a context marked by the crisis of fragmented knowledge. It highlights the contribution of Basarab Nicolescu, who laid its epistemological foundations through the introduction of three postulates: the existence of multiple levels of Reality, the logic of the included third, and the co-existence of objective and subjective dimensions. In the chapters that follow, transdisciplinarity will be viewed as a response to reductive thinking and contemporary hyperspecialisation, proposing instead a framework of complex thinking and the unity of knowledge. Rather than embracing simplifying reductionism, this endeavour inaugurates a new world in which the human, the real, and science co-exist in a responsible, anticipatory, and plural manner.