In this article, I aim to reflect upon and offer insights for the delimitation of the political concepts of ‘left’ and ‘right’ for the purposes of historical research. The guiding motive of this exercise is to highlight the need for prior historiographical and conceptual work before incorporating either of these concepts into historical investigation as objects of study. In this article, I present the fundamental criteria and identity markers that allow us to define the two concepts and, briefly, the importance of Conceptual History as a methodological approach for clarifying the object of study. I conclude the article by putting forward a proposal for the delimitation of the two political fields in contemporary Portugal.