The last two decades have witnessed a remarkable growth of interest in what are variously termed discourse markers or discourse particles. The greatest area of growth has centered on particles that occur in sentence-initial or turn-initial position, and this interest intersects with a long-standing focus in Conversation Analysis on turn-taking and turn-construction. This volume brings together conversation analytic studies of turn-initial particles in interactions in fourteen languages geographically widely distributed (Europe, America, Asia and Australia). The contributions show the significance of turn-initial particles in three key areas of turn and sequence organization: (i) the management of departures from expected next actions, (ii) the projection of the speaker's epistemic stance, and (iii) the management of overall activities implemented across sequences. Taken together the papers demonstrate the crucial importance of the positioning of particles within turns and sequences for the projection and management of social actions, and for relationships between speakers.