This chapter provides discussion on linear optical spectroscopy. The most widely performed experiments in linear optical spectroscopy are transmission-, reflection- and luminescence spectroscopy. Other techniques include e.g. photoluminescence excitation spectroscopy, ellipsometry, measurements of the luminescence yield or Raman spectroscopy. The most descriptive informations regarding the above techniques are stated. The standard set-up for linear optical spectroscopy consists of a light source, the sample under investigation, frequently placed in a cryostat, a monochromator or spectrometer to disperse the light, a detection unit and a PC to handle and evaluate the data. For the spectral dispersion of the reflected, transmitted or emitted light grating monochromators or spectrometers are almost exclusively used in the visible, near UV and near IR. The "waveguide" geometry to allow for multiple pass of the probe light through the quantum structure with a significant component of the electric field vector normal to this quantum well structure has been shown.