This paper reviews the basic properties of the infrared free-electron laser FELBE at the Forschungszentrum Rossendorf. At present FELBE delivers pulses with typical durations of 0.9-5 ps in the wavelength range 4-22 gμm, which soon will be extended to 150 μm. Furthermore we report on recent experiments using FELBE, namely the study of phonon resonances in ferroelectric domains using a newly designed scattering scanning near-field optical microscope (s-SNOM), as well as pump-probe spectroscopy on doped semiconductor superlattices. The pump-probe signal reflects, apart from a component due to the bleaching of the interminiband transition, the temperature of the miniband electrons on a picosecond timescale.