  We derive a general expression for the threshold resummation of transverse
momentum distributions for processes with a colorless final state, by suitably
generalizing the renormalization-group based approach to threshold resummation
previously pursued by two of us. The ensuing expression holds to all
logarithmic orders, and it can be used to extend available results in the
literature, which only hold up to the next-to-leading log (NLL) level. We check
agreement of our result with the existing NLL result, as well as against the
known fixed next-to-leading order results for the Higgs transverse momentum
distribution in gluon fusion, and we provide explicit expressions at the
next-to-next-to-leading log level.
