abstract: Property T of a group G is a fixed point property of actions of G on Hilbert spaces. It was introduced by Kazhdan in the 1960's in a most influential 3-page paper. We study and prove a higher analogue of property T for arithmetic groups which is formulated in cohomological terms. Earlier related results often relied on deep analytic and number-theoretic results. Our novel method is based on results of geometric group theory such as isoperimetric inequalities in groups. Joint work with Uri Bader.