What is the American or European Expiry? American and European options have similar characteristics but the differences are important. For instance, owners of American-style options may exercise at any time before the option expires. On the other hand, European-style options may exercise only at expiration. Although most equity options are American style options, many broad-based equity indices, including the S&P 500, have actively traded European-style options. Related articles What is At The Money Options? What is the Black-Scholes Model? What is a Butterfly Spread? What is a Gamma Profile? What is Charm?