  This thesis summarises my scientific works in the field of thermo-chemical
modelling of planet-forming discs since 2009, in particular the development of
the Protoplanetary Disc Model (ProDiMo). By combining chemical rate networks
with continuum & line radiative transfer, and the calculation of all relevant
dust and gas heating & cooling rates in an axisymmetric disc structure, these
models make detailed predictions about the molecular composition of the disc,
the discs' internal gas and dust temperature structure, and the composition of
ice layers which form on the refractory dust grain surfaces. The development of
ProDiMo was a process that took about 15 years. I have started the ProDiMo
project and am the main developer, but without the involvement of an
international team of scientists, in particular Inga Kamp, Wing-Fai Thi and
Christian Rab, ProDiMo would not have its capabilities and would not be at the
level of international recognition that is has achieved to date.
  Using formal solutions of the line & continuum radiative transfer, we can
predict the spectral appearance of these discs from optical to millimetre
wavelengths, for example the continuum and line fluxes, monochromatic images,
radial intensity profiles, high-resolution line profiles that probe the disc
dynamics, visibilities and channel maps. A large part of this thesis describes
the publications that compared these predictions to disc observations that have
been obtained by various space-borne and ground-based astronomical instruments,
in particular Herschel/PACS, Spitzer/IRS, VLT/CRIRES, JWST/MIRI and ALMA. These
observations probe the gas and the dust in different radial disc regions and in
different layers above the midplane. This thesis summarises the conclusions
drawn from the ProDiMo thermo-chemical disc models about the chemical and
physical state of protoplanetary discs as the birth places of exoplanets.
