  Planck is the third generation of mm-wave instruments designed for space
observations of the cosmic microwave background (CMB) anisotropies within the
new Cosmic Vision 2020 ESA Science Program. Planck will map the whole sky with
unprecedented sensitivity, angular resolution, and frequency coverage, and it
likely leads us to the final comprehension of the CMB anisotropies. The Low
Frequency Instrument (LFI), operating in the 30-70 GHz range, is one of the two
instruments onboard Planck satellite, sharing the focal region of a 1.5 meter
off-axis dual reflector telescope together with the High Frequency Instrument
(HFI) operating at 100-857 GHz. We present LFI and discuss the major
instrumental systematic effects that could degrade the measurements and the
solutions adopted in the design and data analysis phase in order to adequately
reduce and control them.
