Using Irish case law a starting point, the paper argues the principle of certainty is relevant in the context of hate crime in three key ways. First, in the context of the legislative definition of protected characteristics (i.e. does reference to “race” in a statutory provision, for example, include bias articulated against the national origin of the individual). Second, a number of statutory provisions (eg, in Sweden, New South Wales, New Zealand and as recommended by ODHIR) include a ‘proviso’ whereby the court is entitled to consider ‘similar characteristics’ to those articulated in the legislation when determining whether a crime was hate motivated. Finally, in the absence of any legislation, the use of judicial discretion to consider a hate element as aggravating a sentence. The paper will explore these specific contexts, and consider the application of the principle to hate crime generally.