The present paper will treat the function of Theme in the Spanish clause from a systemic functional perspective. This function is part of the textual metafunction, located in the lexico-grammatical stratum. It is the most relevant function of the system of THEME, according to the definitions by Halliday ([1979] 2002). The main goal of the paper is to establish the means by which this function is realised in Spanish. This issue is controversial (e.g. Arus, 2010, 2017; Lavid, Arus & Zamorano, 2010 vs. Moyano, 2016), so that it is relevant to clarify the theoretical elements that orient the position sustained and to substantiate this position through text analysis. To do this, the paper states an interpretation of the functions of Theme and New based in SFL classic literature. Then, proposes a trinocular methodology to orient the description of these functions in Spanish (Caffarel, Martin & Matthiessen, 2004a; Martin, Quiroz, Wang & Zhou, in press). Eight texts are analysed in order to conclude that the unmarked Theme in Spanish is realized by agreement with the verbal affix while the marked Theme by position. Finally, a system network will be drawn and explained before the final reflections.
