We show that the Mobius disjointness (i.e. the Sarnak conjecture) holds for a large family of interval exchange transformations T of 3 intervals. This is done by showing that for most distinct primes p and q there are no joinings of T^p with T^q. However, we show that there are uncountably many ergodic joinings of T with itself. This is joint work with Jon Chaika.