  This paper presents an overview of several modeling tools for analyzing
molecular line observations at submillimeter wavelengths. These tools are
already proving to be very valuable for the interpretation of data from current
telescopes, and will be indispensable for data obtained with ALMA. The tools
are: (1) the Leiden Atomic and Molecular DAtabase (LAMDA), a collection of
spectroscopic data and collisional excitation rates; (2) RADEX, an on-line and
off-line program to calculate non-LTE excitation and emission from a
homogeneous medium, based on the escape probability approximation; (3) RATRAN,
an accelerated Monte Carlo program to solve molecular excitation and radiative
transfer in spherical and cylindrical symmetry. The paper presents examples of
how to use these tools in conjunction with existing data reduction packages to
quantitatively interpret submillimeter single-dish and interferometric
observations. The described tools are publically available at
http://www.strw.leidenuniv.nl/~moldata .
  The paper concludes with a discussion of future needs in the fields of
molecular data and radiative transfer.
