Scholars have shown that codified constitutions may be amended informally with similar effect as a formal amendment. Yet the many forms of informal amendment are not well organized for analysis and comparison. In this article, I examine the forms of informal amendment, I classify them as either conventional and unconventional forms of informal amendment, and I subsequently introduce an as-yet underappreciated and undertheorized form of informal amendment: constitutional desuetude. Constitutional desuetude occurs when a codified constitutional rule loses its binding quality upon political actors as a result of its conscious sustained disuse and public repudiation by preceding political actors. Constitutional desuetude both resembles and differs from other forms of informal amendment: it is similar because it changes constitutional meaning without altering the constitutional text yet it is different because it renders the constitutional text politically invalid though it remains codified and unchanged. I draw from the Constitution of Canada to illustrate the phenomenon of desuetude.