  The search for complex organic molecules in the interstellar medium (ISM) has
revealed species of ever greater complexity. This search relies on the progress
made in the laboratory to characterize their rotational spectra. Our
understanding of the processes that lead to molecular complexity in the ISM
builds on numerical simulations that use chemical networks fed by laboratory
and theoretical studies. The advent of ALMA and NOEMA has opened a new door to
explore molecular complexity in the ISM. Their high angular resolution reduces
the spectral confusion of star-forming cores and their increased sensitivity
allows the detection of low-abundance molecules that could not be probed
before. The complexity of the recently-detected molecules manifests itself not
only in terms of number of atoms but also in their molecular structure. We
discuss these developments and report on ReMoCA, a new spectral line survey
performed with ALMA toward the high-mass star-forming region Sgr B2(N).
