The thesis analyzes and discusses Jürgen Habermas’ political philosophy, focusing on his theories of multiculturalism and deliberative democracy. This implies an assesment of strengths and weaknesses in Habermas' theory, and an attempt to overcome the weaknesses through some revisions and reinterpretations. More specifically, I apply Habermas' framework to a particular question to which he himself has not paid systematic attention, namely how we should justify and use free speech in culturally diverse democracies. The first part of this question (how to justify free speech) pertains to how we should justify constitutional free speech as political philosophers. Here, I advocate robust free speech guarantees, based on a reading of Habermas' normative theory of (reflexive, political, and private) freedom. I argue that legal regulations of hate speech (i.e. racist speech) may be legitimate, but not regulations of blasphemy and religious offense. The second part (how to use free speech) pertains to the citizens’ use of free speech in culturally diverse contexts, and thus transcends the focus on mere legality. Here, I argue that the same concern with freedom that justifies free speech as a constitutional right also limits free speech - in a pragmatic and moral sense. The pragmatic sense refers to how hate speech and misrecognition harm the social preconditions for freedom, in particular the freedom of members of weak or marginalized groups. The moral sense in which freedom limits freedom refers to norms of equal recognition that guide (or should guide) public deliberation between persons who respect each other as free and equal. Even though the imperative of equal recognition does not require us to recognize others' cultural identities or respect their religious feelings as such, it does require us to take their cultural attachments into account when interacting - and deliberating - with them.