  These lecture notes emerged from a contribution to the "Les Houches Summer
School, Session CVII - Current Trends in Atomic Physics, July 2016". It is
meant to serve students as a guide to a selection of topics that are currently
at the focus of molecular quantum optics and complements an earlier lecture on
related topics [Arndt et al., 2014]. In this review we discuss recent advances
in molecular quantum optics with large organic molecules. In particular, we
present successful experiments of molecules of biological importance, such as
neurotransmitters and map out the route towards interferometry of large
bio-matter such as proteins. The interaction of internally complex molecules
with various beam splitters is discussed for both far-field diffraction at a
single nanomechanical grating and the Kapitza-Dirac Talbot-Lau near-field
interferometer - addressing recent progress, experimental challenges, and
prospects for quantum enhanced metrology of highly complex systems in the gas
phase. A central part of this review deals with the preparation of slow beams
of neutral biomolecules, ranging from a single amino acid to proteins or
peptides in a micro-environment.
