Internet filters can be understood as any method that “[blocks] content [from] coming into and going out to the Internet” (PC Magazine, n.d., para. 1). Instantaneously, the word ‘blocks’ causes advocates of intellectual freedom to stand at attention. The American Library Association’s (ALA) Library Bill of Rights states: “a person’s right to use a library should not be denied or abridged because of origin, age, background, or views” (as cited in Houghton-Jan, 2010, p. 40). More specific to the topic at hand: “the use of Internet filters to block constitutionally protected speech … compromises First Amendment freedoms and the core values of librarianship” (ALA, n.d., para. 1). This paper will investigate and discuss the function of and methodology behind internet filters, with specific attention to their application in Canada. Following a general overview, a discussion follows of what library professionals in public and school libraries should do to uphold and protect intellectual freedom.