This chapter examines the issue of how well Canadian jurors comprehend legal instructions and whether there are jury aids that can enhance their comprehension. It traces the design of the first study in Canada to assess the relative efficacy of two competing styles of instructions used in Canada and to compare them with the plain language criminal law instructions used in California, USA. The style that used a series of logical questions to be answered was associated with the highest levels of comprehension. The results also revealed that the type of aid provided had a modest impact on overall comprehension score and that those who received either both aids (written instructions and decision trees) or written instructions had scores that were significantly different from either those with no aid or the decision tree alone. This chapter also explores some of the challenges associated with cross-jurisdictional research. Additional studies are needed to ensure that jurors have an accurate understanding of the law and to make clear how styles of jury instruction and jury aids can impact comprehension levels.