We present a modal logic of belief and announcements in a multi-agent setting. This logic allows to express not only that ψ holds after the announcement of φ as in standard public announcement logic (PAL), but also that the announcement of φ occurs. We use the logic to provide a formal analysis of several concepts that are relevant for multi-agent systems (MAS) theory and applications: the notions of communicative action (an agent informs another agent about something) and communicative intention (an agent has the intention to inform another agent about something), and the notion of information source.