Allyl ethers of enols and phenols undergo rearrangement to C-allyl derivatives when heated to sufficiently high temperatures. The reaction, named after its discoverer (Claisen, 1912) was first observed when ethyl O-allylacetonacetate was subjected to distillation at atmospheric pressure in the presence of ammonium chloride. The allyl ethers of phenols rearrange smoothly at temperatures of about 200°C in the absence of catalysts, Allyl ethers of ortho-disubstituted phenols rearrange to the corresponding p-allyphenols. The only known example of para rearrangement accompanied by inversion is the reaction of alpha-ethylallyl 2-carbomethoxy-6-methylphenyl ether. These rearrangements are discussed in detail.