EN
To any bounded analytic semigroup on Hilbert space or on $L^p$-space, one may associate natural 'square functions'. In this survey paper, we review old and recent results on these square functions, as well as some extensions to various classes of Banach spaces, including noncommutative $L^p$-spaces, Banach lattices, and their subspaces. We give some applications to $H^∞$ functional calculus, similarity problems, multiplier theory, and control theory.