The far IR or THz spectral region, which lies below 400 cm-1, is important for the study of inorganic substances which involve vibrations of heavier atoms. External or lattice vibrations, which are sensitive to crystal structure and polymorphism, can be seen also for both inorganic and organic solid samples. VERTEX 70v FTIR spectrometers offer a wide band mid to far-IR beamsplitter and detector combination to access the complete spectral range in one go (VERTEX FM option). ATR (Attenuated Total internal Reflectance) is a very popular technique in the mid IR because neat samples can be studied without any time consuming preparation which may also change the nature of the sample. Furthermore, certain ATR sampling accessories can operate in far IR because of their all reflective optics.