The present study is framed within the methodology of Conversation Analysis (CA). It uses naturally occurring interactions in Mexican Spanish to investigate six Spanish particles: turn-initial no, pues, 0 sea, oye, ah, and ay. These particles are treated as sequential markers (SMs). That is, the analysis focuses on the sequential and social implications of these particles in interaction. The questions that this thesis aims to answer are: what do speakers do when deploying these SMs in terms of actions in talk, and what do these SMs do to the structure of the interaction or/and to the interactional activity? To answer these question, each SM is examined individually and their examination is carried out in very specific type of sequences or interactional environments: turn-initial no is analysed in assessment sequences and in environments of activity transition. Pues is analysed when it prefaces the answer to a question or a request or an agreement; and when pues is deployed at the end of a turn. 0 sea is examined in environments of repair and topic shift. Oye is analysed in sequential contexts that shape the structure of conversation, and when it is deployed at the end of a turn. Ah is examined in informing sequences and in three different sequential contexts where speakers display remembering. Finally, ay is analysed with relation to the talk that precedes it. This study attempts to illustrate how SMs are significant features of the organization of talk and the accomplishment of actions in interaction. It proposes an alternative approach, i.e. CA, to the study of Spanish particles - so called marcadores del discurso (,discourse markers'). And it aims to initiate the investigation of Spanish interactions using CA as a framework.