The strategy used for forming polar questions varies across languages. While in some languages, polar questions are formed using a raising intonation, in others, polar questions are formed using an interrogative particle. This paper focuses on a type of interrogative particles which has not received much attention in the semantic literature. I call these particles polar interrogative particles. On the empirical side, I identify the signature properties of polar interrogative particles, and show that we need to draw a distinction between (at least) three types of interrogative particles cross-linguistically. On the theoretical side, I develop a full-fledged semantic analysis of these particles and of the questions where ther occur. The proposed account contributes to a better understanding of the source of presuppositions in questions and their projection behavior, and of the interaction between different sets of alternatives (namely, question and focus alternatives).