A material adverse effect (MAE) or material adverse change (MAC) clause may be found in a wide variety of agreements, including share and asset purchase agreements used in mergers and acquisitions (M&A) transactions, arrangement agreements, loan agreements, underwriting agreements and commodity derivative contracts. This Practice Note considers, from a Canadian common law perspective, how MAE and MAC clauses have been interpreted in Canada and how they are likely to be interpreted in the future, in light of US case law.