When discussing focus particles, it has been common practice to rely on the dichotomy of inclusive vs. exclusive particles, à la König (1991). Inclusive focus particles are often further divided into scalar particles, such as also, too, and either, and non-scalar particles, such as even. In this thesis, I advance a comparative analysis of the major inclusive focus particles in English, which reveals more complicated pictures of the particles concerned. I show that also and even share far fewer properties than previously assumed. It turns out that also is additive, anaphoric, and anti-scalar, while even is non-additive, non-anaphoric, and scalar. This finding suggests that the traditional classification of focus particles need to be reconsidered, through more in-depth investigation into the semantics of individual particles. In addition, the realization of the disparity of the two English particles leads one to cast doubt on the widely accepted view that Korean focus particle -to is ambiguous between the readings of also and even. Using the same criterion as with the English particles, I provide a univocal approach characterizing -to as additive, not anaphoric, and underspecified with respect to scalarity. Another finding in this descriptive study is that other than being focus particles, also, even and -to shares one important role: they impose meta-propositional constraint on the propositions involved. I posit the Parity Condition and the Co-Support Condition for also, and the Non-Entailment Condition and the Co-Argumentation Condition for -to. As for even, I argue, in the footsteps of Kay and Ducrot & Anscombre, that its scalar implicatum is a meta-propositional operator relating the proposition expressed by the sentence containing the particle and a non-monotonous inference supported by this proposition. Finally, I discuss the information status of the three particles, and conclude, against the presupposition approaches, that the existential implicata conveyed by also and -to contributes to the assertorical content of the sentence containing them, and maintain the traditional view, à la Grice, that the scalar implicatum invoked by even is a conventional implicature.